Dallin McAllister, 25, of Utah, and Tyler McAllister, 36, of Arizona, are each charged with operating a motor vehicle in prohibited areas and feeding, touching, teasing, frightening or intentional disturbing wildlife.
Both men appeared in federal court in Yellowstone before Judge Kelly Rankin and pleaded not guilty.
A video posted to a Facebook group shows motorcyclists in a field within feet of bison and their calves. Visitors to Yellowstone National Park are required to stay 25 yards from bison.