WWF said the raid last week in the coastal nation of Gabon also included 30 chimpanzee hands and body parts belonging to leopards, elephants and a lion. If convicted, though, the suspects only face up to six months in prison.
Officials said they did not know what the body parts were intended for.
"Heads and hands, for example, are sometimes used for ritual ceremonies," said Natalia Reiter, communications manager for WWF International. "Some people believe it would bring them luck and some just keep it as souvenirs. Hands are believed to bring more power or are used as trophies."
Wildlife officials believe the case spans far beyond Gabon's borders as lions are not native to the country, so those animal parts originated elsewhere. The suspects are also all from elsewhere in Africa - four Nigerians and a woman from Benin.
"We don't know yet where these were going to be sent to in this case," she said.
WWF African Great Ape Manager David Greer said the haul was "highly disturbing."
"To my knowledge, there has not been a seizure of great ape body parts of this magnitude in Central Africa over the last ten years," he said.
Bushmeat - the meat of gorillas, chimpanzees, elephants and other endangered and exotic species - is consumed and sold throughout sub-Saharan Africa. The practice is fueled by extreme poverty that forces people to poach for the meat.
However, the meat also has a market in Europe, where it is consumed by African immigrants. One study last year found that more than five tons of bushmeat slips through the main airport in Paris alone each week.
Reiter said the five suspects in Gabon are being held by authorities while an investigation is conducted. They are expected to appear in court this week.
But she said the arrests are only part of the fight against animal poaching and trafficking.
"We really need to target the dealers, as they are the ones who are selling them everywhere in the world," she said. "Unfortunately there are a lot of markets for leopard skins, ivory and other wildlife so it is an international operation."