That could be a sign that your power outlet isn't grounded properly. I have two outlets in my house that are grounded "differently" than the rest of the house. If I connect a piece of electronics to that outlet, then touch it, I get zapped. If I plug the same piece of electronics into another outlet, no zap. (The most obnoxious part is that the outlet closest to our TV is one of the two, which means any time I want to plug or unplug anything, I get a little zap.)