Ethiopia has arrested thousands of members of the Oromo ethnic group over the past three months, according to Amnesty International.
The government has been cracking down on protesters
The London-based human rights group said students were among those who have been rounded up since November.
Amnesty said the arrests follow protest calls by the rebel Oromo Liberation Front against alleged government fraud.
The government has denied the claims as "misinformed and incredible."
An information ministry statement said that "86 student suspects who are arrested for throwing bombs at schools, breaking school property and disrupting the teaching and learning process are charged at pertinent courts... in compliance with the laws of our country".
The Amnesty report warned some of the detainees may be "at risk of torture or ill-treatment" and called for their release.
November's demonstrations in the southern Oromia region followed a call by the OLF for anti-government protests.
Opposition groups have accused the government of rigging last May's elections.
Amnesty said among those arrested were school students, teachers, farmers and, businessmen.
"Those detained have reportedly been accused of links with the OLF, although none of them has yet been charged," it said.
It called on Ethiopian authorities to either charge or release the detainees and investigate alleged mistreatment of some of those held.
Meanwhile, the US-based Committee to Protect Journalists (CPJ) said Frezer Negash, an online journalist for the Ethiopian Review, had been arrested on Friday and was being held without charge in Addis Ababa.