Ok thanks. Is there a possibility that this could cause damage to my iMac?Check your ground connection on the outlet.
Use a voltage test that tests all 3 lines (hot, neutral & ground).
Most common problem is that the hot/neutral is reversed or the ground is missing.
Then check you power cord using a DMM/DVM for 3 lines continuity.
If all that has been checked, the power supply inside may be the culprit...
No it should not. There is no electrical connection from the incoming power or neutral return to the case. If this was the case it would never pass the various electrical safety standards around the world.If you're in a country that just uses a 2-prong plug (NO ground), then you may very well feel a slight "tingling" when the Mac is plugged in. Laptop users complain about this as well.