First Officer reported a brake fire event was caused by grease dripping down on hot brakes after arriving at the gate. Ground personnel extinguished the fire with no other issues.

Narrative

Captain landed flaps 30 brakes 3 in ZZZ around 145;000 pounds and stopped normally for a rather short taxi back to the gate. Landing was normal in Touch Down zone and on speed. Brakes seemed to work normally and did not chatter when we came to a stop at the Gate. Parking and checklists were complete when we started to retrieve flight plans for the next flight. A ground support personnel came up to the flight deck and said; 'you know you are on fire right?' The Captain was already off the flight deck and told the last remaining 4 passengers and the 4 flight attendants (FA) to get off the aircraft. The APU was running with no fire indication; however we had no ground power; so I delayed shutdown as there was no evidence of fire and I wanted to ensure we had radios to call for crash fire rescue (CFR). I ran to the back as the FAs were delayed deplaning because there was a passenger waiting for his younger brother to get off the airplane (which had not previously been visible). The Captain ran downstairs to see what was on fire and initially was told we had smoke coming from a pitot tube; but was then show the number 2 brake smoldering. The fire was out; but we had gotten the rest of the passengers and FAs off while we determined whether or not we needed CFR. A fire truck was in between our aircraft and the plane next door; which lead me to believe CFR had already been called. The fire truck was actually paramedics for the other flight. At this point; there was no fire and we called Maintenance. I coordinated with ground personnel and the Captain released the parking brakes to aid with cooling. After about 15 minutes; the tire slowly deflated. The next days Maintenance Release stated that grease had leaked from a dust seal and was the source of the fire. Both wheels and brake assemblies were replaced and we flew the aircraft back to ZZZ1 uneventfully.