Did you jsut have a baby? Sometimes after having a baby you get a dark blood type thing going on down there. All that is is old blood in your uterus. If it continues I would contact my doc. Are you in pain? If there is pain, make it asap.
You're not providing enough information. How old are you? What day of your cycle? Brown blood is usually old blood.
I have had brown spotting before.. often it is just old blood!! if it persists or happens multiple months in a row there's no harm in headin to the doctors just to get checked!