This 36-year-old constable was on her way to Witbank in her Toyota RAV4 where she would've allegedly delivered 7kg of dagga, said Leonard Hlathi, police spokesperson.
Two women (respectively aged 40 and 45) who were also in the car, were also arrested.
The three women were caught on Friday night after police received a tip-off. Three bags of dagga were hidden in the engine compartment.
One of the suspects ran away just after they were stopped.
The police's dog unit searched through the bushes next to the road and found the woman hiding in the long grass.
Hlathi said one of the suspects admitted to selling dagga. "I won't stop selling dagga," this woman apparently told police at the scene.
"Dagga sales have kept my children in school."
The three women are expected to appear in the Nelspruit Magistrate's Court on Monday.