It can be funny to see dogs chase their tails. Short episodes of infrequent tail chasing can be seen when dogs are very excited or happy. It can be a way of releasing some of that excited energy. Some dogs may chase their tail if they have a tail injury or in attempts to groom themselves.
However, it is abnormal for dogs to consistently chase their tails.
This can be an attention-getting behavior to start. But with time, this can lead to OCD or compulsive behaviors and can interfere with normal behavior and activity. This can cause problems for the pet and the pet parents. If your dog is excessively chasing its tail, then consult with your veterinarian on behavioral modification techniques and possible medication to help with the management of stress and OCD.