One victim was hit in the eye and the other was wounded slightly in the arm.
The Ada County Sheriff's Office said the shooting occurred shortly before 3 p.m. local time at the Fort Boise Gun Show at Expo Idaho in Garden City, the Idaho Statesman in Boise reported.
Deputies said the person who picked up the handgun didn't realize it was loaded and unintentionally fired it into a display, the newspaper said. Deputies said the bullet hit two other guns in the display and shrapnel hit the two bystanders, including a 23-year-old Mountain Home man who was hit in the eye.
He was taken to a hospital and was expected to survive.
The second victim who was hit in the arm was treated at the scene.