Navalny wrote that he was released until a court hearing, but did not provide details on when the hearing would be held. He also thanked demonstrators who had gathered near the detention center where he was being held.
Navalny, a longtime critic of President Vladimir Putin, was arrested earlier Sunday during nationwide rallies protesting what the opposition leader calls rigged presidential elections set to take place on March 18.
"I've been detained. This doesn't matter. Come to Tverskaya (Street). You are not going there for me, it's for you and your future," Navalny tweeted after his arrest.
Within minutes of arriving at Pushkinskaya Square, where hundreds of protesters had gathered, Navalny was wrestled into a patrol van by police, in dramatic footage posted on Youtube.
Moscow Police said Navalny was taken to a police station for arraignment on charges of illegally organizing a protest. If found guilty, he faces 30 days in detention and a fine.
Coordinating protests in the largest country in the world by land mass is no small task, and the Russian Interior Ministry said events coordinated with local authorities were held in 46 places.
Demonstrations have ranged from gatherings of a few dozen in remote areas to about a thousand people in central Moscow -- which the Interior Ministry described as an "uncoordinated mass demonstration."
Protesters also turned out in arctic areas of the country, where the temperature during winter is around -40 degrees, said CNN's Fred Pleitgen in Moscow.
Elsewhere, there were 600 demonstrators in Russia's third-most populous city, Novosibirsk, and 550 protesters in Nizhny Novgorod in western Russia, the ministry said.
"I am proud of all those who joined us today in any capacity: from Magadan to Sochi. From the FBK office to the headquarters in Kemerovo. From Krasnodar to Yakutsk, where the meeting took place at -40. These are real citizens," Navalny said in a Facebook post.
"Be real citizens. Go out to the demo in your city."/CNN