The anus should not be bleeding. You should see a doctor immediately. When are you noticing signs of blood? If it is during anal sex, you may just have a tear, and you should see a doctor as they can give you some ointment to settle it down.
If you notice rectal bleeding for any other reason you need medical attention as soon as possible. Typically bright red blood can be coming from anywhere in the anus, bowels and gastrointestinal tract, depending on what is causing it, you may or may not have other symptoms.
Could be hemroids, torn tissue from passing hard stools (especially if you've been constipated. You need to go see a doctor though as it could be a sign of more serious issues like bowel cancer etc.