As others have said, he is probably cutting his molars and the biting helps to relieve the pressure, however that is NOT an excuse to ignore biting!
With my son (he's 2.5), we treat biting like hitting and kicking, as very serious offenses. We do not (ever) 'play' bite, hit or kick, not even in jest. My son is also not allowed to do those things to his stuffed animals, because when they are young, children see their stuffed animals/dolls as other people, so they should learn to treat their toys with the same respect they would show a person.
As others have said, you should make an effort to give him appropriate things to bite, like the old frozen washcloth trick from when they were little (the gel teething rings can't be used after they have teeth), but certainly don't hesitate to discipline the biting, even if it's just his bear. Nip it in the bud now, and you won't have issues later.