Existing mole has crusty wart-like surface

Have had a normal round raised brown mole on my arm for many years approx 6mm diameter. Recently the surface has become crusty like a scab, now has wart like appearance. It has not grown and does not itch or hurt. GP says doesn't think anything sinister but have been referred to dermatology. Can a normal raised mole crust over like this without being malignant?