The bus was traveling south Friday night on Interstate 24 about a mile (1 1/2 kilometers) from the exit for the festival when the man stepped onto the highway, said Melissa McDonald, spokeswoman for the Tennessee Department of Safety.
His identity was not released, pending notification of his family.
McDonald said it was unknown if the man had been attending the four-day festival, but his identification showed he was not from Tennessee. It appeared the man jumped over a fence to reach the highway, she said.
The accident is still under investigation. There was no indication of alcohol use by either the bus driver or the victim, McDonald said.
Calls to Skaggs' representatives late Friday were not immediately returned.
The Bonnaroo festival is in its fifth year, attracting about 80,000 music fans and artists each year to 700 acres (280 hectares) of farmland in central Tennessee about 60 miles (100 kilometers) southeast of Nashville.