My Japanese Chin dog don't bark?

I have a healthy Japanese Chin dog name Gizmo, but he just doesn't bark. When ever he hears other dogs he only picks his ears up. The only times he barks is when his at sleep. Is a really really low bark (he only does it like 2 or 3 times) and also wiggles his tail :) so i know that's good. but should i be worry?