Nhlanhla Lux Dlamini, the leader of a South African anti-migrant protest movement, was apprehended on Thursday, according to police.
The number of attacks on foreigners in South Africa, notably Nigerians, is on the rise.
Hundreds of Nigerians have fled the nation as a result of the threat of violence.
Nhlanhla Lux Dlamini, 30, was arrested and escorted to the central police station in Johannesburg for questioning.
Dlamini, a black activist, is well-known in his neighborhood for driving a high-end sports car.
He is also noted for his public appearances, which he does virtually every day while dressed in military fatigues and a bulletproof vest.
Members of his organization reacted angrily to the arrest, threatening to escalate their activities on social media.