7 segment display with common anode
This answer assumes Arduino Uno. For other types, refer to the documentation.

Ardino pins are not positive per se: you can change the voltage with digitalWrite() to either 0V (LOW, equal to the GND pin) or 5V (HIGH, equal to VCC). 

The difference between a common cathode or common anode will be the flow of the current. With a common cathode (negative), the pins will need to provide current ("source" current), with a common anode, the pins will need to receive current ("sink" current).

There is a description for the limits of sourcing and sinking:


  Pin SOURCE Current Limitations:
  
  20 mA at VCC = 5 V
  
  Pin SINK Current Limitations:
  
  20 mA at VCC = 5 V


Please also read about the maximum total of 150 mA sourcing and 100 mA sinking.

You'll need to compare those current limits with the current requirements of your 7 segment display. My guess is that your a 7 segment display has 1 VCC pin and 7 output pins that you connect to the Arduino. The limiting factor is the total maximum here. The Arduino can handle 100 mA/7 = 14mA in the worst case. If that's enough for your 7 segment, it should work.

For example, this one works with 10 mA, so it would be compatible with Arduino. Make sure you have resistors in place.