Lindsay suggested great advice on the neutering recommendation.
This type of behavior is common in dogs - I'd like to offer you a few tips on how to deal with the behavior.
Do not make a big deal when he does this. The more attention you give to him, the more times he'll offer this behavior. Just ignore him, walk away if you have to.
You can also try to re-direct his behavior. If you can catch his attention right before, grab a favorite toy or treat that he REALLY likes. Encourage him to play or take a few treats from you.
If he only humps the teddy bear, I would put the old bear away for some time. After he's neutered or after a month or so, bring ol' teddy back out and see if his "habit" has stopped.
It's not the most attractive behavior to see our dogs display but it is natural. If you would like any other information we are more than happy to continue helping you!