How can electricity be positive when electrons are negative?
First before answering what I think is truly your question, I will have to beat into you how voltage are relative:

An atom has protons in the nucleus which is orbited by electrons. If the numbers are equal, then the positive and negative charges cancel out and the charge is zero.

Suppose we start with two terminals. Each terminal has a net charge of zero there are the same number of orbiting electrons as there are protons in the nucleus at both terminals). That also means neither terminal is positive or negative relative to each other.

If you rip some electrons off the atoms in one terminal and shove them into orbits around the atoms in the other terminal, then the terminal that lost electrons becomes more positive and the terminal that gained electrons becomes more negative relative to each other.

So the positive charge is due to protons and the negative charge is due to electrons, BUT what is important is that you understand that the protons DO NOT MOVE, not independently of the nucleus anyways (that would be a nuclear reaction). You do not produce a positive charge by moving protons around

You produce both positive and negative charges by moving electrons around to mess with the imbalance of electrons and protons. As a result, it is often more useful to think about a positive charge as a deficiency of electrons rather than an excess of protons since you are manipulating electrons, not protons.

NOTE: Some people have pointed that hydrogen ions, basically just the nucleus of hydrogen which is just a proton, can move around just fine and carry a positive everywhere they go. They can, but the difference here is that the proton was already free. It was not ripped from a nucleus and then relocated in order to move a positive charge from place to another. That ripping action is a nuclear reaction.

If you had three different terminals:


One with a balance of protons and electrons
One with fewer electrons than protons.
One with more electrons than protons.


Then #2 would still be more positive than #1, and #3 would still be more negative than #1, even though #1 doesn't have an excess of anything (net charge of zero). It's all relative.

That means that if you had three terminals:

A. One with a balance of protons and electrons

B. One with more electrons than protons

C. One with even more electrons than protons.

Then B would be positive relative to C, but negative relative to A. It's all relative. Whether something is positive or negative is entirely dependent on what you are measuring it with respect to.

The voltage of something relative to itself is always zero, because it's like measuring sea-level with respect to sea-level. It doesn't matter what sea level ends up being, it is always equal to itself so the measurement relative to itself is always zero.

Now, to address your actual question:
We don't say electricity is positive. We also don't say a battery is positively charged. Don't forget a battery has both a positive AND a negative terminal, and everything is relative. 

What is more likely to be happening is that the ground/0V in your circuit was chosen as the point of reference against which all other voltages were measured. Then the negative terminal of the battery was connected to this point, and people don't always want to say "relative to ground" all the time, so they just say the battery is positive. It's completely possible to have a second battery in the circuit where the positive terminal is connected to ground to provide a negative power supply.

When analyzing most circuits we tend to follow the current flow as if electricity is positive charges moving when in reality is is electrons (which have a negative charge) that are flowing. 

This is because early scientists assumed the charge carrier was positive early on and by the time they figured out their mistake it was too entrenched and would take too much work to fix so it stuck. It doesn't matter for most circuits because most circuits have electrons moving through a sea of nucleui that have protons present so it is mathematically equivalent that a positive charge moves in the opposite direction of the negative charge.

But it matters in some things where this mathematically equivalency is not the case such as vacuum tubes and semiconductor physics where it actually does matter that a negative charge is moving.

For example in a wire, you have those copper nuclei containing protons providing that positive charge whenever there is no electron to balance it out to produce a net charge of zero. So mathematically, electrons move in the opposite direction of the positive charge produced by "absence of the electron". It is the "absence of the electron" that moves in the opposite direction of the electron (not the proton because the proton doesn't move.) But in a vacuum tube you have a vacuum. There are no or nuclei or protons in that vacuum. When an electron moves away, there is no proton left behind to produce a net positive charge. You literally have a negative charge carrier (the electron) moving through the vacuum.

It's dumb. I hate it.