Prince, 18, was joined by his grandmother Katherine Jackson, sister Paris Jackson, and several other relatives, reported Us magazine.
"When they announced his name, the whole Jackson family stood up and cheered and whistled. Prince was ecstatic as he crossed the stage and picked up his diploma," an eyewitness said.
The onlooker added that Prince's family sat in the front row for the ceremony and the graduate posed for photos with his loved ones at the reception.
His younger sister Paris, in particular, seemed "very proud" of him.