These are either mites or fleas. Go to the pet supply store and get some Revolution. This will kill both types of parasites. Frontline and Advantage will only kill fleas - not mites, so use the Revolution. You only have to treat your cat once a month and it will also take care of ear mites and intestinal worms also.
Please let me know if I can help further.
Feline Healthcare
16 yrs health care mgmt & issues relating to cats, reproductive issues and multicat environments