I have this problem with one of my cat, he bites when I am petting him and playing with him. I think I know why mine is bitting is because he is declawed on all four paws so that is his only defence he has. I don't know how you stop his biting bu if he isn't biting to hard maybe he wants to play and you could say no that hurts then release your hand but don't yell at him or try giving him a toy to play with instead of your hand.