I would place money on these NOT being spider mites, they would be all over the plant, and not the pots themselves.
Usually, you spot spider mite damage on your plants BEFORE you would actually see any spider mites..so really have a good look on your plants for any tiny dot damage, also check under the leaves for any pests.
They actually look like beneficial mites in the photo you provided..which you would want to keep around as they eat spider mites!