Yes, Medusa's head continue to have power after it was detached from her body by Perseus. In fact, upon beheading Medusa two offspring came out from the drops of her blood- Pegasus, a winged horse, and Chrysaor, a giant or a winged boar. Perseus also used Medusa's head as weapon in most of the fights he had and later on requested to place Medusa's head into his shield.