IMO, it is normal…but still not acceptable. Get a treat...start to lure him off the seat, before he starts to carry on. Give it a command, like 'get down' or 'off'. Then start to use your command, and treat after he gets down. Pretty soon, when you walk in he will be hopping off to get his treat.
It might or might not progress to biting. Some dogs are just mouthy little monsters...they bitch and moan about everything....but some are giving you a clear warning...stop doing what you are doing or I will escalate.
Good luck, and let us know how it goes.