Jason Segel was caught on set with some huge stars this weekend -- The Muppets!

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Kermit the Frog, Miss Piggy, Gonzo, Beaker, Janice and Bunsen were all seen this weekend in downtown L.A. filming a new movie, which Segel helped write and is starring in.

We're just happy to see 'em all back in action -- check out the set photos!