Friends discovered the body of Eric Ohena Lembembe at his home in the capital, Yaounde, on Monday evening after he was unreachable for two days, the rights group said in a statement Tuesday.
One friend said Lembembe's neck and feet looked broken and that he had been burned with an iron.
Lembembe was among the most prominent activists in one of Africa's most hostile countries for sexual minorities. First as a journalist and later as executive director of CAMFAIDS, a Yaounde-based human rights organization, he documented violence, blackmail and arrests targeting members of Cameroon's gay community. He was also a regular contributor to the Erasing 76 Crimes blog, which focuses on countries where homosexuality is illegal, and he wrote several chapters of a book released in February on the global gay rights movement titled "From Wrongs to Gay Rights."