Moscow's Simonovsky district court ordered that Leonid Volkov be detained in police cells for five days.
The protests on June 12, a public holiday in Russia, saw more than 1,700 protesters detained nationwide, some of whom were later fined or sentenced to several days behind bars.
Navalny, a charismatic 41-year-old lawyer, has announced his intention to stand in elections in 2018 that President Vladimir Putin is expected to contest.
Navalny is currently serving a 25-day sentence for violating rules as the organiser of a demonstration after being arrested outside his home as he was heading over to the Moscow protest.
Volkov was found guilty of breaking rules on organising a public event after he hosted a live YouTube feed on the protests in various cities from the office of Navalny's team of anti-corruption investigators.
In court, he said he was simply commenting on the protests, some of which went ahead without permission from the authorities.
Volkov said in court that he was "hosting a live broadcast of protests" from 6:30 am until 3:30 pm local time, Interfax news agency reported.
"I don't believe I did anything wrong," he said.
"I'm not the organiser of the protests, I was just working as a journalist like many others."
Volkov also told the court he warned Navalny's supporters that if they attended the unauthorized protests, it was at their own risk.
He was handed a summons to appear in court by police live on air Wednesday evening as he held another YouTube broadcast.
Eyewitness? Submit your stories now via social or:
Email: news@pulselive.co.ke
