The Annie Hall star stunned The Tonight Show host Jay Leno when she interrupted his interview and dashed off to pick up the scruffy mutt, called Clover, backstage.
Keaton, who is on the board of a shelter in California, asked if any member of Leno's studio audience wanted to take the dog home.
She said, "I knew I was gonna go on Jay's show and I saw this dog... I thought maybe somebody in the audience might wanna rescue Clover. Clover needs a home... Are there any bidders?"
Ironically, Keaton's new movie, which she was on the show to promote, is all about a couple which rescues a stray dog.