Depends on how badly its frayed, if its just a bit on the side you can get your craft on and hand stich it up pretty well. you can also put a patch over a bigger area. (you can usually buy seatbelt stuff from a craft shop, or just stop by the wreckers)
Mind you, neither of these solutions are road-worthy over here.. not too sure about Canada. And it will also really affect the safety of the seatbelt..
Better to replace it, but yes you can make a minor repair to patch it up and look a bit better untill you do replace it.