Law enforcement sources tell TMZ ... a burglar forced open a backdoor and entered Kevin's home. The actor was not there. The thief stole an antique gun and some other minor items before beating it.

Kevin was notified of the break-in and met the cops at his home, where they took a report.

Cops reviewed surveillance footage from the area and determined the suspect appeared to be a homeless man and not a member of the burglary rings that have been targeting high-dollar homes around L.A. in recent months.

TMZ broke the story ... thieves smashed a window at Keanu Reeves' home this month and stole his Glock.