A large explosive device was found outside an apartment block in Metamorphosi, northern Athens, on Friday before it went off.
Explosives had been placed in a 30-liter container, which also contained three detonators, according to police who are examining the bomb for clues.
Officers did not provide further details about the potential victim or motives for the attack.
Police have arrested six people four men and two women - on the island of Elafonisos on suspicion of breaking antiquities, firearms and explosives laws.
Officers searched several homes before making the arrests.
They seized almost 16 kilos of explosive material along with other equipment needed to detonate it.