Is it a recent purchase? They could've come with the T from wherever you bought it from. This goes for feeders too. Keep an eye on him/her and hopefully they don't multiply. There are lots of methods for removing individual mites from your T but I'm not sure about the mouth area.
I'm not 100% sure on molts clearing the spider of mites but I'd assume the molt would take care of them if it's only a few. Maybe someone with more experience can chime in.
I'm probably the biggest worrier in this forum when it comes to mites. But I'm learning that they're pretty unavoidable in small numbers and simple cage maintenance with proper ventilation is what keeps their numbers from exploding and causing real problems.
My biggest concern though are feeders carrying them.
No its too deep, and its eating. This is the first time I have gotten a good look since the fangs are spread so wide. I have fed a few slings mealworms for the first time since last week. I don't know if the mites came from them.