The court said Navalny, an outspoken critic of President Vladimir Putin and a leader of anti-Kremlin protests in 2011 and 2012, had violated rules barring him from leaving Moscow.
Navalny denounced the ruling as baseless and said it was meant to silence him. Supporters, including members of protest band Pussy Riot, shouted “Freedom!” as he left the courtroom.
“I believe the new measures are based on trumped up grounds in order to restrict my political activities,” Navalny, 37, said in court.
Kremlin opponents say the upheaval in neighbouring Ukraine, where protests forced President Viktor Yanukovych from power after he scrapped plans for closer European Union ties to move closer to Moscow, has deepened Putin’s determination to prevent any revival the earlier street demostrations.
They say Putin is also clamping down on dissent after engineering the release of long-jailed oil tycoon Mikhail Khodorkovsky and two members Pussy Riot before the Sochi Olympics, which ended last week.
Navalny, who gained prominence with blog posts alleging government corruption, emerged from the biggest protests of Putin’s 14-year rule as the main opposition leader and a potential future challenger in elections.
He is serving a five-year suspended sentence on a theft conviction that will keep him out of a 2018 presidential vote, and has been charged with theft and money-laundering in a separate case that has not come to trial.
Under the terms of his house arrest, which expires on April 28 but is renewable, he is barred from using the Internet and telephone and can only speak to close relatives, his lawyers and the authorities, his spokeswoman Anna Veduta said on Twitter.