The 28-year-old has been charged with the premeditated murder of Mokoena, who was killed in April last year.
Mokoena’s charred remains were discovered in an open veld in Lyndhurst, Johannesburg.
The trial was postponed last month due to the emergence of new evidence.
At least 20 witnesses are expected to testify in the state’s case against Mantsoe.
He has denied killing Mokoena, but admitted to disposing her body during his bail application.
CCTV footage from Mantsoe’s apartment allegedly showed that they had been together on the night she went missing.