Twenty members of the Afrikaner extremist group Boeremag, or white farmer force, last year were found guilty of treason for a plot, in the late 1990s and early 2000, to violently overthrow the country's government.
The African National Congress formed the country's government when Mandela was elected to office in 1994 to bring an end to white minority rule.
Judge Eben Jordaan handed out the sentences in Pretoria to end the decade-long trial. Some sentences were suspended due to time served, according to reports by South African TV channel EnCA.
The leader of the group and four members of its bomb squad were given some of the longest sentences. They planted a bomb on a road Mandela was going to take for a visit to a school in Limpopo Province, but the plot was foiled when the anti-apartheid leader changed plans to take a helicopter to the school. Having already served 10 years, those getting the heaviest sentences will serve 25 more, according to the South Africa Press Association. Another member of the squad was given 20 years, with 10 suspended, SAPA reported.
This was one of South Africa's longest running trials and it was one of the most expensive costing the country about 36 million rand (USD 3.6 million), according to the non-governmental group, Legal Aid.
Boeremag is an extreme group of Afrikaners, the white South Africans of Dutch, French and German descent who ruled the country under the racist apartheid regime that ended in 1994. The guilty include former engineers, medical doctors and military officers.