This type of bleeding may be caused by haemorrhoids. These can develop because of low fibre in your diet, becoming constipated therefore straining when you go to the toilet, amongst other things. They can be removed/deflated by non-surgical procedures which are in most cases very effective.
I also agree with the other comments that the bleeding can be caused by polyps and so on, but as a matter of urgency you should really go and get it checked out. This type of thing is a very serious matter and shouldn't be left to chance that it might go away.