Natalya Estemirova's body was found in Ingushetia, which borders Chechnya to the west, Oleg Orlov, the chairman of Memorial, her rights group, told The Associated Press.
Estemirova's corpse was discovered with two close-range bullet wounds in her head not far from the region's main city, Nazran, said Ingush Interior Ministry spokeswoman Madina Khadziyeva.
Earlier, Orlov told the AP that four men forced Estemirova into a car in the Chechen capital, Grozny, on Wednesday. He said witnesses heard her yell that she was being abducted.
Estemirova, a single mother in her early 40s, had collected evidence of human rights abuses in Chechnya since the start of the second war there in 1999.
She also worked with the investigative journalist Anna Politkovskaya, another critic of Russia's war against separatists in the Caucasus. She was gunned down in her Moscow apartment building in 2006.
Estemirova also worked with Stanislav Markelov, a prominent lawyer and opponent of rights abuses in Chechnya, who was shot and killed on a Moscow street in January.
Wednesday's killing comes as violence spirals in Russia's North Caucasus, with Ingushetia being particularly hard hit in recent months.