Hi there! It seems your lab puppy is showing some signs of aggression or maybe, you might not notice it, he just wants to play. Puppies his age doesn't show that much aggression specially if he is not confident with his owner being mad at him when he behaves badly. It's the proper time to show him some manners too when he does behave bad like barking on the wrong place and the wrong spot. There's a good read about this topic on this page
http://dogobedienceadvice.com/aggression-in-puppies.php.
Tootchie's Mom
