I think you're talking about the electrostatic charge on the metal parts of the iPad as it is charging?
If so, it's normal -- it happens Apple's metal laptops to varying degrees as well, if you are charging with a 2-prong charger.
It's caused by the charger not being grounded. If you use a 3-prong adapter, the static charge will go away. It's a phenomenon known as "leakage".