They would appear in court soon, Captain Kay Makhubela said. A ninth person ran away during the arrests.
Protesters had barricaded the Soweto Highway since 03:00 on Thursday, in a protest against evictions in the area.
Makhubela said Johannesburg metro police chased them away as they were advancing on a Metrorail train station in the area. Broadcaster eNCA reported that signalling infrastructure on the Naledi-Johannesburg line was damaged.