Police said the bomber had intended to enter the court in the northwestern town of Shabqadar, near the Mohmand ethnic Pashtun region, and set off his explosives when guards challenged him, Reuters says.
Television news footage showed extensive damage including the charred remains of at least two vehicles.
Senior police official Sohail Khalid told Reuters two police personnel, as well as four women and two children were among at least 10 people killed. Nearly 30 people were wounded.
The Pakistani Taliban's Jamaat-ur-Ahrar faction claimed responsibility for the attack in the town, about 150 km (90 miles) northwest of the capital, Islamabad, according to the report.
Group spokesman Ehsanullah Ehsan said in an emailed statement the bombing "was especially done as vengeance for the hanging of Mumtaz Qadri".
Qadri, a bodyguard-turned-assassin, was executed last week for killing Salman Taseer, the then governor of Punjab province, after he had called for reform of blasphemy laws that mandate death for insulting Islam or its prophet.
