The bomber threw hand grenades before detonating a suicide vest among the morning crowds at the court, senior police official Faisal Shehzad told AFP. "At least ten people were killed," he said, including two policemen.
No group has yet claimed responsibility for the attack, which comes three weeks after a massive suicide blast killed scores of lawyers in the southwestern Pakistani city of Quetta, in Balochistan.
Pakistan's legal community are frequently the subject of targeted killings and small-scale attacks by militants, who are also known to hit soft targets such as schools.
Militants on Friday also launched an attack on a Christian colony in the Khyber Pakhtunkhwa provincial capital of Peshawar, 60 kilometers (37 miles) to the west of Mardan.