Perfectly normal, but annoying, behavior for a pup his age. In addition to the above suggestions, you could head off some of this by knowing his schedule and giving him some good exercise. Pups this age need tons of exercise several times a day. So, try to anticipate this behavior and before it occurs take your boy out for a good walk, run, or other exercise. Wear him out and he'll be interested in napping rather than grabbing.

Another thing you can do when he begins to act up is to have him follow a command by asking him to sit, lie down, etc. If he responds to the command, reward him with his exercise routine.

Exercise several times a day, if you have time, is not too much especially for a pup this age. Hang in there - it will get easier!