Sounds as if they might be Springtails. Can't be sure without a photo, however the description fits
These can be normal much as mites can be in some worm bins if conditions are favorable. They are simply there assisting in decomposing.
One way to determine if they are springtails is if they jump when disturbed as they have a little mechanism under the belly that enables them to jump.
I found a picture of the springtails
Hope this helps to identify them.