"Alexei has been detained in the stairwell", his wife Yulia wrote on his Twitter account about 40 minutes before the anti-corruption rally called by the Kremlin critic was set to start in the city centre.
The 41-year-old's anti-corruption videos have needled the country's most powerful and drawn to the streets crowds unseen since a wave of protests against President Vladimir Putin's reelection to a third term in 2012.
The scale of the protests will show if Navalny can build on the success of a similar event in March, in which thousands took to the streets across Russian Federation.
The prosecutor's office has warned police will take action against any unauthorised demonstrations.More news: Numbers drawn for 10th largest lottery jackpot
Russian opposition leader Alexey Navalny was detained by police outside his apartment in southern Moscow after calling on supporters to mount an unsanctioned protest near the Kremlin, his supporters said.
President Vladimir Putin vowed to punish people who broke the law after an estimated 60,000 people protested in March at anti-corruption rallies organized by Navalny that were mostly unsanctioned in 80 cities across Russian Federation, the biggest unrest in five years.
Mr Navalny said contractors hired to build a stage at the agreed-upon venue could not do their work.
Around the venue for the planned protest, on Tverskaya Street in central Moscow, hundreds of riot police and military conscripts were waiting.More news: Stanley Cup Final tightens up
This was a reference to the main thoroughfare in central Moscow, near the Kremlin, where the protest was getting underway Monday afternoon.
Eleven demonstrators were arrested in Vladivostok, according to OVD-Info, a website that monitors political repressions.
Navalny, Russia's most prominent opposition figure, has been arrested numerous times for a variety of accused crimes. His report on alleged corruption connected to Prime Minister Dmitry Medvedev was the focus of the March protests.
While Putin has yet to confirm his candidacy for the March 2018 polls, chief critic Navalny is already on a whistlestop tour of Russian Federation, opening campaign offices and trying to collect the 300,000 signatures needed to enter the race - despite doubts he'll be allowed to stand.More news: 'The Mummy' turns out to be Tom Cruise' biggest mistake
For now, polls suggest Navalny has scant chance of unseating Putin, who enjoys high ratings. In April, he suffered damage to one eye after an attacker doused his face with a green antiseptic liquid.