If a cat has warm ears, it can indicate a fever. The ears, along with the pads of the feet, help to regulate the animal's temperature.
If the cat has been laying in the sun or another very warm spot, it can also cause the ears to become warm. To determine if the warmth is a result of a fever, check for other symptoms, including a dry, warm nose. The cat's temperature can also be checked using a thermometer. If the cat has a fever, or other signs of illness, it is best to consult a veterinarian to obtain the correct diagnosis.