Is this Behaviour a cause for a trip to the vet?

My dog keeps dragging her backside, rubbing her rumb on the floor. (in a seated position and moves herself forward with her front legs). I will sometimes have streaks of ****stains on the floor as a result of this. Is there something wrong with her? Should it be a concern to bring her to the vet? I am worried it might be a symptom of some disease. My friends told me that some dogs just happen to have this very bad habit and there is nothing physically wrong with her. If this is so, how i can break this bad habbit?