Our dog does this as well. With our dog, it usually means she wants us to go outside with her for some reason. She likes to be outside but gets lonely and is looking for someone to hang out with her, or play with her, etc. Also, sometimes it means she got spooked by something (usually a loud sound that she's not familiar with, etc.) and she's a little scared to go out by herself. Once we step outside with her for a few minutes she relaxes and is OK to stay outside by herself. The other day, she wanted to go out desperately but wouldn't step out of the doorway until I went with her . . . then she promptly threw up. It was like she needed a comforting presence because she wasn't feeling well. Just like my kids when they aren't feeling well . . .
Generally, though, our dog is fairly relaxed during the day because we make sure she goes for a nice walk for about an hour each evening after dinner. I think it helps a lot! And in the mornings I usually take her in the car (which she loves!) when I drop my daughter off at school. Our dog likes to be engaged and only gets "ansy" when she has too much energy. Dogs can self-entertain to an extent (chew toys, etc.) but they are also social creatures so they like to interact with their humans as well. And if they don't get enough interaction . . . you wind up with a restless, "yappy" dog.