South Africa's counter terrorism unit has arrested 19 suspected Congolese rebels in northern Limpopo province, police have said in a statement.
The group was not specified but the police said their believed objective was the overthrow of the Democratic Republic of Congo's government.
M23 rebels, who began an uprising in eastern DR Congo last year, have been in talks with the Kinshasa government.
Some 800,000 people have fled their homes due to the violence.
The alleged rebels are due to be charged in court in the capital Pretoria later on Tuesday under South Africa's Foreign Military Assistance Act, the police statement said.
The M23 has told the BBC that none of its members have been arrested in South Africa.
There are numerous different armed groups operating in eastern DR Congo.
The M23 rebellion began as an army mutiny last April and the rebels went on to take the eastern city of Goma in November.
They agreed to withdraw under a regionally brokered deal and are involved in halting peace negotiations in Uganda.
Rwanda and Uganda have both denied UN accusations that they have backed the rebels.
Rwanda has been heavily involved in its eastern neighbour since those responsible for the country's genocide fled there en masse in 1994.
The region's mineral riches have been plundered by numerous groups and countries over the past 15 years.