Forte also gained 76 yards on six carries.
Terrell Pryor ignited an Oakland comeback bid in the second half by running for a score and throwing for another. Pryor went 7-of-10 for 93 yards after starter Matt Flynn was 3-of-6 for only 19 yards and two interceptions.
Sebastian Janikowski produced Oakland's' first points with a 58-yard field goal on the final play of the first half.
After the Raiders closed within seven points in the third period, Michael Ford ran 15 yards for a Chicago touchdown with 9:43 to play.
The Bears won their second exhibition game in three tries. Oakland is 1-2.