Brown discharge that doesn't smell unusually bad or isn't associated with unbearable itching is not likely to be anything to worry about. It happens to a lot of women toward the end of their menstrual period. Brown blood tends to be older blood that has been in the body longer (as opposed to bright red blood). Toward the end of a period, when the flow has slowed significantly, a woman often sees brown blood.
You might be experiencing a very light, low-flow period. It is almost certainly nothing to worry about, but if it continues or is associated with pain or severe itching, it's time to see a doc.