"The couple was forced to sit on Jai Kumar's motorcycle, while Mohan Singh drove the boy's bike to an isolated area where they beat the boy and took turns to rape the girl," he said.
After the incident, the couple reported the matter to the police and an FIR was lodged.
Mohan Singh was arrested on Saturday, he said, adding he was sent to judicial custody till March 16.
Another accused Jai Kumar is still absconding and a hunt is on to arrest him, he said.
The girl was living in a rented accommodation in Kota city and attending medical coaching classes.
Both the accused, who are local residents, were the RAC jawans and they were terminated from the services in 2006 for their involvement in a robbery case, the SHO, who is the investigating officer, said.