Is this a puppy? We need more information...Thanks, Karla
You didn't give much information about the dog and the environment.
What age, how long has the problem been going on, have you changed anything in his environment (food, toys, outside exposures....) what is age, how long have you owned him... may be many other helpful item you can share.
If the condition continues, especially if it has other symptoms and exist so that a vet can examine, that is the only way to be sure what the problem is.