My dog is limping on his hind leg, but it does not seem to hurt him when I touch or move it.

Do I need to be worried? Should I wait and see if it gets better?

If a dog is limping on any leg for more than a couple of days, you should have him checked by a veterinarian.  If the dog is limping and you can see that the leg is swollen or hot, get your dog to the vet immediately.