Four people believed to be right-wing extremists were arrested by police in the Free State on Sunday.
According to eNCA, they were allegedly plotting to disrupt the ANC's elective conference in Mangaung.
"The suspects are aged between 40 and 50 years old," said Free State police spokesperson Brigadier Billy Jones.
He said the four people were suspected of acts of terrorism.
"Their premises were searched and evidence supporting the investigation was seized."
Jones said the arrests were the result of a successful joint law enforcement operation.
He said the four would be charged and brought before a court soon.
No further details about the police operation or where the four people were arrested were given.