Navalny was sentenced to house arrest through April 28 and prohibited from using the Internet, Russia's state-supported news agency RIA Novosti reports.
The case stems from allegations he defrauded French cosmetics giant Yves Rocher of $790,000.
No stranger to the Russia courts, opposition leader Navalny last year was suspected of faking lawyer credentials. In 2012, he said Russian authorities were trying to "scare off" activists expressing frustration with President Vladimir Putin.
Anti-government sentiment in Russia escalated in late 2011 when the United Russia Party, once led by Putin, maintained its leadership in State Duma elections. Putin's re-election to a third non-consecutive term as president in 2012 sparked further protests.
Human rights groups accuse the Putin administration of enacting laws meant to silence his critics. The U.S. State Department in its profile of the human rights situation in Russia said the political system is "dominated" by Putin.