Keanu Reeves: Cops Investigate 'Matrix' Obsessed Fan

Keanu Reeves is once again being courted to join the resistance and save humanity ... only this time it's not Morpheus ... it's an obsessed fan who thinks "The Matrix" is real life.

According to legal docs ... the LAPD is looking for a guy who showed up at the actor's home last October and placed a FedEx envelope in his mailbox, offering up a cell phone number with this instruction: "I will call the cell provided tomorrow. We need to meet as I have already started building the new world. #masterbuilder."

Cops believe the guy has an obsession with Keanu's character, Neo, from "The Matrix" movies ... the cell phone reference is actually a nod to the first movie.

Keanu told cops he's afraid for his safety because the guy knows where he lives ... and he thinks the guy suffers from some type of mental disorder.

The LAPD is on the case.