My dog (4yr.old pug) is wobbling. i just noticed it when i got home 20 minutes ago and he's still doing it...?

Look around the house, is there anything the dog has gotten into, like a plant or any substance? If not, it could be nothing but considering the breed and age, the dog could have hurt that particular leg somehow or he may be experiencing mini-strokes, seizures or another neurological disorder. The least of which could be diabetes, which the breed is becoming more and more well known for developing. I seriously recommend you call the vet tomorrow and get the animal seen ASAP. This could turn out to be nothing but most likely it will so have that animal checked out.