Wales international Roberts, 30, will provide half-back cover in the absence of injured trio Will Chudley, Dave Lewis and Niko Matawalu.
Roberts also has Premiership experience with Northampton and Bath.
"The Chiefs are going very well at the moment, so hopefully I can come in and help add to that and get some game time," he said.
Exeter Chiefs have signed scrum-half Martin Roberts on loan from Bristol for the remainder of the season.