Anal bleeding is never normal and should always be investigated. You don't say how old you are. The more serious and sinister causes of anal/rectal bleeding generally only arise above the age of 30-40 and maybe evenb later.
However, unless your doctor is able to confirm that the cause of the bleeding is only from a minor cause - e.g. anal fissure or haemhorroids, then I suggets that you insist on a colonoscopy which is a very comprehensive test and will afford you the maximum reassurance (hopefully).
Good luck
Morecambe
This:
http://www.allhealthsite.com/35/symptoms-and-causes-of-diarrhea/#bloody-diarrhea
How old are you, any previous deisease, other symptoms, how much bleeding, also can you describe it precisely?