The fire did not cause any further material damage to the building but sparked alarm on social media among traumatised Lebanese who have witnessed several fires at or near the blast site since the explosion.
"Tuesday's curse #Beirut. Another Tuesday, another fire," wrote one resident on Twitter, referring to the August 4 explosion that killed more than 190 people and injured at least 6,500 others - and which took place on a Tuesday.
The fire broke out in an office on the second floor of the Electricite du Liban (EDL) building in the hard-hit Mar Mikhail neighbourhood, said Ali Najem, a spokesman for the Beirut fire department.
He said papers in the office had caught fire but that he was not authorised to disclose the original source of the blaze before investigations had been completed.
Charbel Saleh, an EDL employee, said it was a short-circuit fire, adding that it was doused a few minutes after it ignited.
At least two fires have broken out at Beirut's port since the August 4 explosion, prompting widespread anger and alarm.
And on September 15, also a Tuesday, firefighters put out a blaze at a building designed by the late British-Iraqi architect Zaha Hadid that was under construction in the capital's downtown area.