How old is he?
There are many reasons for behaviour like this - stress or just plain bad habits being the main ones. He could just be going through a 'naughty' stage in life, in which he's testing boundaries and needs to be reminded what's right.
If you are sure he is happy with his lot and there's no specific reason for it and he's just being naughty (because it IS a bad habit), you'd better nip it in the bud. The longer you let it carry on the harder it will be to stop. A sharp 'no' or similar noise is good to start with, followed by a short sharp smack if that doesn't work.
A pony we used to have on the yard was terrible for pawing if no one was paying any attention to her - it was just brattishness, she'd paw for a while, staring at you, and when you made any move towards her or spoke to her she's stop and look innocent, starting again as soon as you looked away. We tried everything, even totally ignoring her to the point where she was driving us crazy, until one day the YO lost his temper and threw a brush at the wall next to her. It made a huge bang and she jumped about 3 feet in the air, but she never pawed for attention again.
I'm not saying that's the way to deal with it, but sometimes they need to be switly reminded what isn't acceptable.