It could be a small area that has been mildly burned, usually minor burns won't be too obvious until the snake has shed, when they can sometimes get the white scale appearance. If it is that, in time and given a few sheds it will disappear.
Of course it might also be one of the other suggestions, without seeing the snake in the flesh, it can be hard to say for sure.
If you are worried, do as others have said, take it to the Vets for peace of mind.
Neil