The actor, 49, posted a video on his website professing his love for the 22-year-old "The Help" star.
"I think you're all the way beautiful, not just pretty but smart and kind hearted," Carrey said. "And if I were a lot younger, I would marry you, and we would have chubby little freckle-faced kids."
"We'd laugh all day long and go camping, play Yahtzee, tell ghost stories by the fire. And the sex...," he trailed off, and then added, "And everyday, for the rest of your life, you would thank God that I was the appropriate age for you."
He finished the message with: "Anyway, I just wanted to let you know how I felt. You're pretty special, and I wish you continued success and artistic fulfillment, but most of all, I wish you love and contentment. That's all."
On Twitter, Carrey reassured fans that the video was a joke.
"Yes, my msg to Emma Stone was a comedy routine and the funniest part is that everything i said is tru," he wrote. "Hahahaha! ?;^P"