Video footage posted on social media showed Mr Navalny appearing on Moscow's main thoroughfare, a few hundred metres from the Kremlin, to join several hundred supporters taking part in the nationwide protest, which authorities had said was illegal.
He had only walked a short distance when he was surrounded by helmet-clad police officers.
They wrestled him to the ground on the pavement, and then dragged him feet first into the patrol wagon, the video footage showed.
Mr Navalny's personal Twitter feed carried a post to his followers saying he had been arrested.
"That does not matter. Come to Tverskaya," the post said.