"The car that blew up belongs to Idriss al-Ghadi, an official with the municipal elections committee," said the official who declined to be named.
"The car was parked in a lot outside a school in the Majuri district which is being used as centre for the committee organising the elections," he told AFP.
No one was hurt in the blast but five cars belonging to committee members, who were attending a training session in the school, were damaged.
The eastern city, epicentre of the 2011 uprising that toppled the regime of veteran dictator Muammar Gaddafi, has seen a surge in attacks targeting security forces, judges and foreign missions.