Hukam Khan, the bomb-disposal squad chief, said the bomb contained 3kg of "high quality explosives" and was placed on the front seat of the car.
He said: "Our initial assessment is that it was a time bomb."
The court building has been the venue for regular protests by lawyers since Pervez Musharraf, Pakistan's president, suspended Iftikhar Muhammad Chaudhry, Pakistan's chief justice, on March 9.
However, there were no such event being held there on Tuesday.
"Secret agencies are committing such acts to sabotage our movement against Musharraf," said Qaiser Rashid, a senior member of the Peshawar High Court Bar Association.
Others believe that the bombing was part of an attempt to destablise the provincial government.
Peshawar, the capital of North West Frontier Province, is also close to the Afghan border and has been hit by a rash of blasts in recent months blamed on Muslim groups angry with the Pakistan government's alliance with the US.
Earlier in the week, tribal fighters killed two Pakistani paramilitary soldiers in a suicide bombing on the outskirts of the town of Tank, shortly after fighters killed an officer of the paramilitary Frontier Corps in an ambush in the same area.
The attacks came just hours after police killed four fighters said to be loyal to the Taliban in a gunfight in the town of Bannu, 80km northeast of Tank.