Is there any chance your cat could have fleas, as someone asked?
How long has this been going on for?
Does your cat go outside at all?
Do you have any other pets in the home?
Does your cat have any patches of fur that are missing?
Does kitty seem to be biting at him/herself at all? Scratching?
The more information you can provide us, the better.
If it's definitely not fleas, my thought was like someone else's, feline hyperesthesia:
http://www.purelypets.com/articles/f...eresthesia.htm