Navalny, a long-time critic of President Vladimir Putin, broadcast live video of police entering his Moscow offices.
CNN reached out to the Moscow police, but they said they “have no information regarding the raids”.
The incident comes as Navalny called for nationwide protests and for supporters to boycott presidential elections set to take place on March 18.
Navalny said police sawed through the door of the office’s studio, during a live YouTube broadcast.
“In order to take down our broadcast, the police cut out the door to the Anti-Corruption Foundation (FBK) office, and then began to saw the door to the studio right in the middle of broadcast,” he said in a Facebook post.
“Do you know the formal reason? Dmitry Nizovtsev, the host, was accused of planting a bomb (without actually going off air, we must assume), and it was necessary to cut the doors asap in order to find this bomb.
“And then they detained him. Watch it, it’s a good example of what the Russian police has become.”
All seven members of Navalny’s Moscow offices were detained in the raid, according to the Twitter accounts of Navalny and his staff.
They included the head of Navalny’s Moscow headquarters, Nikolay Lyaskin, who was grabbed by police on his way out of the office, according to Navalny press secretary Kira Yarmysh.
During the raid, police also seized computers and cameras from the office, the Director of Navalny’s Anti-Corruption Foundation, Roman Rubanov, said in a Tweet.
Navalny urged supporters to join the protests later Sunday.
“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,” he said in a Facebook post.
“Be real citizens. Go out to the demo in your city.”
Navalny’s weapon of choice
The biggest protests are expected to take place in Moscow and St Petersburg, yet there has so far been no mention of the demonstrations on Russian state TV.
Instead, Navalny and his supporters have turned to YouTube to get their message out, with over 43,000 people watching his live feed as of Sunday morning.
Who is Alexei Navalny?
Navalny, who is Russia’s best-known opposition leader, was barred from running in the upcoming elections after a 2017 criminal conviction for embezzlement.
Critics say the case against the 41-year-old was politically motivated.
In an exclusive interview with CNN at his Moscow headquarters last week, Navalny accused the Putin administration of being “built on corruption” and warned of growing impatience for political change.
“Putin has been in power for 18 years now,” he said. “People are not ready to wait another six years, then another six, then another.”
The Kremlin has rejected allegations of widespread high-level corruption and has condemned Navalny as a dangerous influence whose calls for protests could plunge Russia into chaos.