Vine user Beefyrhetoric uploaded the following clip from Sunday's Oscars broadcast, just after Eddie Redmayne was announced as Best Actor. In it, you can see Keaton holding a piece of paper, which he then shoves into his jacket pocket.
Keaton was neck and neck with Redmayne throughout awards season. While Keaton took home top acting honors at the for Comedy at the Golden Globes, Redmayne won the Best Actor Golden Globe for Drama, as well as Best Actor honors at the Screen Actors Guild Awards and the BAFTAs. So it's reasonable to believe that Keaton thought he had a good shot to win the Best Actor Oscar.
However, "Birdman" went on to win Best Picture, and Keaton had a moment to speak on stage before the telecast concluded.