Fail Alsynov, 37, is regarded as a hero by many of the region's ethnic Bashkir people for campaigning on behalf of their language, culture and rights.
He led successful protests in 2020 to prevent mining operations on a hill that local people consider sacred, and has spoken out over the war in Ukraine, saying young Bashkir men in Russia's army are being "thrown into the fire" of a foreign conflict.
Several thousand people protested on Wednesday outside a court in the small town of Baymak where Alsynov - whom Russian authorities have placed on a list of terrorists and extremists - was sentenced to four years in a penal colony for stirring ethnic hatred.
He denied the charge, which his supporters said was delayed revenge for his successful environmental campaign that forced the authorities to climb down over the mining plans in 2020.
Rights group OVD-Info said a total of 17 people were being held in custody over Wednesday's rally, where police fired tear gas and hit protesters with batons, and about 10 more were detained at Friday's gathering in the capital Ufa. Officials at the local interior ministry could not be reached for comment.
The Ufa rally was peaceful, with videos on social media showing people dancing and singing traditional Bashkir songs.
Hundreds made their way to a central square despite being warned by police on arrival that they risked arrest for attending an unauthorised public meeting.
News outlet SOTA Vision published footage showing police linking arms in a human chain to clear the way for a bus taking away detained people, as onlookers chanted "Shame!"
Public protests in Russia are very rare given the risk of arrest, especially since the start of the war.
The timing is all the more sensitive given that President Vladimir Putin is standing for a new six-year term in March.
While his victory is not in doubt, analysts say there is pressure on Bashkortostan's regional leader Radiy Khabirov to keep the situation under tight control to prevent embarrassment to the Kremlin during an election campaign.
'ACTIVISTS ARE A PROBLEM'
Bashkortostan, a region of 4.1 million people in the southern Urals mountains where Europe and Asia meet, is one of more than 80 republics and regions that make up the Russian Federation.
The "power vertical" established by Putin does not tolerate grassroots activism, said Gulnaz Sharafutdinova, a professor at King's College London and an expert on Russia's regions.
"Leaders that emerge without control from the Kremlin, in a non-managed way, are seen as a threat," she said, adding that Moscow would expect Khabirov as the regional leader to deal with it. "
He's there managing on behalf of the Kremlin, and for him these activists are a problem."
Khabirov said on Thursday that what he called extremists and traitors were trying to get Bashkortostan to break away from Russia.
Authorities have said those detained earlier in the week could face long jail terms. Kremlin spokesman Dmitry Peskov told reporters that there were no "mass riots" or "mass protests" in Bashkortostan, and the situation there was entirely a matter for local authorities and law enforcement.
Ruslan Valiev, a Bashkir journalist now living in Berlin, told Reuters TV that only a tiny minority of Bashkir people are bent on secession from Russia.
But he said there was deep popular support for Alsynov and concern over the issues he had raised, including the disproportionate number of ethnic minority men being sent to fight in Ukraine.
Unofficial figures compiled by journalists showed that about 1,350 men from Bashkortostan had been killed in action, he said - more than in the Afghan war of the 1980s and the Chechen wars that followed the collapse of the Soviet Union.
But local men, faced with poor job prospects and lured by high army salaries, were still signing up for the military.
"I think that the unrest will continue in one form or another, be it something active in the streets or more quietly in the kitchens or backyards," he said.
"Something will keep happening. This issue cannot be simply swept under the carpet."
(By Mark Trevelyan LONDON, Jan 19, Reuters; Additional reporting by Roman Churikov; editing by Philippa Fletcher)