Males and females both do this --- and - neutered and spayed dogs also do it.   It's not a sexual thing -  It is a dominance - ranking - nonsexual - play behavior.   Whatever!    
The important thing is that it is not a desired activity for a little puppy or any dog to do.  Stop it every time you see it happening.  It's a "No no." 
Tell your dog, "No," - move him - distract him - and stop him from doing it.  If he has any toys that he likes to hump - take them away from him.     
Some people think it's cute!  It's not!     
Good luck with your little humper.   I've gone through this with all my dogs.   
One was in love with a stuffed dog - the other was having a love affair with a stuffed rabbit.  And, now my new little Yorkie pup loves my other dog.  There's no end.   I just tell my pup "No no" - move him - and get him doing something else.  He could care less!  But there's a lot less humping going on.     
Carol Jean        |