Electricity consumption of a disconnected electricity socket
First, understand that this "radiation meter" is a piece of junk that has no scientific basis for the numbers it is reporting. It is a device designed to scare you into buying "protective" equipment you do not need, and it is deliberately miscalibrated and  exaggerating wildly

There is certainly an electromagnetic field around any live wire, and a small amount of power is indeed lost when that field induces eddy currents in nearby conductors. That's so far below the amount of power used by anything you would actually plug in that it's effectively zero on the scale of what you're paying for, even when you consider the whole house rather than one outlet. But it is possible to pick it up with suitable equipment -- noncontact testers of several types are a standard tool in an electrician's kit -- and your meter is apparently picking up that signal but lying to you about how strong it is.