Mark Trollip, John Martin Keevy, Johan Hendrik Prinsloo and Hein Boonzaaier appeared in the Bloemfontein Magistrate's Court, the Mail & Guardian reported. Prosecutor Shaun Abrahams said the four were involved in a conspiracy to shoot Zuma and others "execution style" during the ANC's conference in Mangaung.
Abrahams said the killings were planned for Sunday, the anniversary of the Battle of Blood River. On Dec. 16, 1838, a small group of Voortrekkers -- Boers moving into the interior of South Africa -- defeated thousands of Zulu fighters.
Prosecutors said the group had a stockpile of arms.
The four were ordered held without bail pending another hearing Jan. 8.
Francois Cloete, head of the new Federale Vryheids Party or Federal Freedom Party, told the Mail two of the defendants are members of the group.
"We as the Federal Freedom Party still believe they are innocent because the story of the police is constantly changing," he said. "The police must now finally confirm to the FVP what they have been arrested for."