Alfredo Romero, who heads the Penal Forum group, said Josue Farias died in the western city of Maracaibo from a gunshot injury sustained during an anti-government protest nearly a month ago on May 29.
Farias was an accounting student at a Zulia state university.
Demonstrators have taken to the streets to march against rampant crime, runaway inflation and shortages of basic goods in the country with the world's largest proven oil reserves.
Government authorities have yet to add this latest death to its own official count of those who died in the sometimes bloody protests.
In their latest report on June 11, they counted 42 deaths and 873 people injured in the demonstrations that have decreased in intensity in recent weeks.
Efforts to resolve differences between the government and opposition through dialogue have faltered in the wake of the arrest of more than 200 students last month, when authorities demolished protest camps.
Venezuela, an OPEC nation, is struggling with inflation near 60 percent, as well as rampant crime and shortages of goods as basic as toilet paper, milk and sugar.
Most economic experts blame the South American country's problems on a decade of rigid currency and price controls, as well as rising debt, dependence on imports and stagnant growth.