Wuilly Arteaga, 23, had become one of the best-known faces of protests against Venezuelan President Nicolas Maduro, playing the National Anthem as tear gas enveloped him and rubber bullets flew around him.
Anti-government protests have rocked Venezuela for four months, leaving more than 110 people dead.
Arteaga was detained during a protest on Thursday, said Alfredo Romero, head of the Penal Forum rights group, in a Periscope video filmed while driving. Arteaga has become emblematic for government critics of security forces' tough tactics against protesters in recent months.
"They burned his hair with a lighter, beat him very hard meaning that he can't hear through his right ear," Romero said.
The government did not immediately respond to a request for comment.
The young violinist was severely injured last week while playing during protests. Paramedics attended Arteaga on Saturday as blood poured down his face.
He later tweeted a video from hospital with a bandaged face and clutching his violin.
"Neither rubber bullets nor pellets will stop our fight for Venezuela's independence," Arteaga said in the video. "Tomorrow I will be back in the streets."
More than 4,800 people have been arrested during four months of anti-government unrest, according to Romero, with more than 1,300 still detained.