"In Vnukovo!" wrote prominent opposition activist Lyubov Sobol on Sunday, in a translated tweet.
"Greetings to all from Vnukovo. Came to meet a friend here," wrote fellow opposition activist Ruslan Shaveddinov, in a translated post on Instagram.
Navalny supporters and members of his team have been detained by police at the airport, according to subsequent reports and posts on social media.
Video tweeted by @SvobodaRadio showed Lyubov Sobol being detained.
Navalny is traveling from Berlin to Moscow after recovering in Germany from his poisoning in August with a nerve agent. The opposition leader said he was "very happy" as he boarded the plane.
He announced Wednesday that he would return, despite Russian authorities' threats to put him behind bars again. On Thursday, Russia's prison service said he faces immediate arrest once he returns.
"We fly home," Navalny wrote in a translated tweet at 9:12 a.m. ET on Sunday morning, with a link to a short Instagram video of the opposition leader and his wife Yulia Navalnaya on the plane.
"Flew," wrote Navalny spokeswoman Kira Yarmysh in a translated tweet with an image of the opposition leader surrounded by photographers on the plane.
Moscow’s Vnukovo airport, where Navalny’s flight is due to land, last week said it is banning journalists from its terminal, citing epidemiological concerns.
Twitter user @VVPynka tweeted that a high opaque screen has been erected at Vnukovo’s international arrivals hall ahead of Navalny’s arrival.
Navalny, who has blamed his poisoning on the Kremlin, charged that Russian President Vladimir Putin was now trying to deter him from coming home with new legal motions. The Kremlin has repeatedly denied a role in the opposition leader’s poisoning.
At the end of December, the Federal Penitentiary Service, or FSIN, warned Navalny that he faced time in prison if he fails to immediately report to its office in line with the terms of a suspended sentence and probation he received for a 2014 conviction on charges of embezzlement and money laundering that he rejected as politically motivated. The European Court for Human Rights had ruled that his conviction was unlawful.
The Associated Press contributed to this article.
Follow James Rogers on Twitter @jamesjrogers