A large section of the building caught fire in the incident but firefighters were able to prevent the flames from spreading and no one was injured, the report said.
The brewery's vats of the dark "Rochefort" beer also escaped the blaze.
The monks who had been having their evening meal when the fire broke out immediately evacuated the abbey of Notre Dame de Saint Remy-Rochefort.
The abbey in southern Belgium was founded in the 13th century and the monks have brewed beer there since the end of the 19th century.
Francois Bellot of the abbey told RTL-TVI Television he was confident that it would be possible to resume production within a few days.