The slow movement and white color makes me think that they may be a type of oribatid mite, especially if they're round. They're often found in compost bins and feed on decaying plant matter and other organic debris. If they run away when disturbed or spring into the air they're likely springtails, which also feed on decaying organic matter and are desirable in bioactive terrariums. Either way, they're unlikely to be dangerous to your frog at all. I would keep a close eye for population spikes and continue to make sure they aren't bothering the frog by crawling on his face and whatnot.