Hold a piece of white paper under the tree and tap the leaves over it. If the specks fall off and leave red streaks when you smear with a fingertip, you've got mites.
They really dislike being misted. There are different methods of control, including dormant sprays, oils, pyrethrin or something stronger like isotox or malathion. You can learn more at
bonsaiTALK Links if you type in SPIDER MITES or look under Pests & Disease there.
This spider mite link, in particular is pretty good:
http://www.evergreengardenworks.com/mites.htm
Usually the mites leave behind a very, very fine webbing particularly around the new growing tips. Stray strands may just indicate the presence of a common spider, which is a companion most bonsai trees tend to have.
Regards,
Matt