Some women will have some brownish discharge just prior to a period and/or just after a period ends. It is just part of the remaining lining that was built up in the uterus.

If it happens well after a period has ended, it could be from the use of birth control pills, or other hormonal contraceptives, a bit of older blood mixed with semen after sex, or hormone changes during your cycle.

If you get it frequently, and can't attribute it to any of the above, you could always check with your doctor to have an exam.