Whenever my MacBook Air is connected to the AC power and I have my hands on the palm rest, I feel it passes some electricity to me. If I unplug it from the AC power it stops doing that.

This has recently became obvious, when other people can feel this tingling by touching my skin after I've been working for a while.

I have two questions:

1- Is this normal in unibody Macs?

2- Is this harmful for my health in the long run?