Neo, Trinity and whoever the hell Neil Patrick Harris is playing are plugging back into the "real world" for the 'Matrix 4' -- 'cause they're back on set, and cameras are rolling again.

Leading man Keanu Reeves along with his costar and on-screen lover, Carrie-Anne Moss, were both spotted in Berlin this week and presumably heading to their trailers, as they looked ready to get back into character and start filming, after several months off due to 'rona.

NPH was there too. He's one of the big names who was cast in the 3rd sequel ... still unclear what his role will be. Either way, dude seems geared up to kick ass and dodge bullets.

Now, the last time we saw Keanu and co. was earlier this year in San Francisco -- where the freedom fighters were revisiting another federal-looking, bank-ish type building ... reminiscent of the first flick when Morpheus (Laurence Fishburne) was being held captive by the agents.

Speaking of him ... we haven't seen him on set yet. One person we HAVE seen time and again nearby -- KR's girlfriend, Alexandra Grant.

Sure enough, she was there in Berlin as well ... laughing it up with Keanu and some of the crew members. It would appear they're still going strong after making their red carpet debut late last year.