The white flakes on a cat's coat are usually dander, which is a normal product of the cat's skin metabolism. Flakes are made up of shed skin cells, usually white in color, and under normal circumstances will not be closely attached to the skin. In some cases, white flakes may be an abnormal increase in dander due to dry skin, malnutrition, skin disease, parasitic infections or other health problems. For example, ringworm (a skin condition caused by a fungus) in cats can result in round or oval ringworm patches on the skin covered with flakes.
If your cat's dander is accompanied by other symptoms, such as redness of the skin, hair loss or excessive licking of the fur, you should consult your veterinarian for professional treatment.