It is normal for your cat to have dandruff from time to time.  Cats need to get rid of dead skin cells like most mammals.  Since they have fur, their dandruff is generally easy to spot.  Some cats will produce a little, some a lot.  This can be a perfectly normal thing.  However, you may try a few things to see if the dandruff subsides.  Don’t let your cat sit out in the sun too long, especially when it’s really hot.  The dandruff could be a symptom of sunburn.  Also don’t let your cat sit at the fireplace constantly (to prevent skin drying out).  Try pet shampoo, check for parasites, and make sure your cat isn’t overweight or suffering from lack of nourishment.  If this doesn’t help, and you’re still worried, see a veterinarian.