The rat in dreams a very unpleasant omen for those who dreamed about it, but it doesnt have a very bad meaning. The rat is an indicator of the jealous people you are surrounded by. Someone wishes you bad, however you are not in contact with those people, therefore there is no danger for you. If you see the rat that is in white colour, then it means you will get the support from one particular person you never expected to help. If you see many rats running, you shouldnt do whatever you are doing and should concentrate on one issue which would make you happy. It also could mean that you are running from something.
Read more about dreaming of Rat in other dream meanings interpretations.