I haven't seen a flea since I moved to Minnesota from Missouri, though they could probably survive on an animal or in the house. I would be very surprised to see one show up in the middle of winter though especially. If he truly does have fleas, he will have more than one. Where one flea is, there are plenty more. Have him lay on his side and inspect his belly, underarms, behind his ears, etc. carefully. If he has fleas there should be telltale signs, besides little brown bugs (and if you look very closely they are small shiny brown bugs) that skuttle away when you uncover them, he would also have little black grain-like material here and there on his skin, the flea droppings. I'd make certain he actually has them before treating him, it could have been a little gnat or something.

Hopefully he does not have them. Fleas are a huge pain to get rid of from both the dog and the environment. Advantage worked well on the collies, but we also had to spray the yard and flea bomb the house. Even in Missouri though, they did not really show up in the winter... Cats can be one of the worst carriers of fleas, so if you have a lot of stray/feral cats around it's a possibility they are spreading their fleas around. There were a lot of stray and feral cats where I grew up in Missouri. It made the battle to keep fleas down very difficult.