Navalny's wife, Yulia, reported news of his detention at his home in Moscow on his official Twitter feed. She also posted a picture showing police officers at the scene.
He had planned to attend a rally in the capital, but is now facing a possible 30-day jail term, according to a post on Twitter by his lawyer, Vadim Kobzev.
State news agency Tass confirmed he had been arrested, reporting that he faces allegations of violating laws governing demonstrations.