The boy was riding his bicycle when a dog became aggressive and bit him several times in the shoulder and upper arm, Carroll County Sheriff Tobe Leazenby said.
A young friend saw the attack and screamed, which caused the dog to flee back to its property, he said.
The boy was taken to a local hospital with torn flesh and several puncture wounds. He underwent surgery about 7 p.m. Thursday.
"Based on the initial feedback we're receiving from family, he will come through OK," Leazenby said. "But the injuries were somewhat graphic, from what I understand."