Twenty-eight-year-old Thomas Dyer and 29-year-old Tanya Humboldt were driving into Neillsville on Highway 73 Wednesday. Dyer, who was driving, was injured when the bomb exploded beneath his seat.
Agents from the U.S. Department of Justice's division of Alcohol, Tobacco and Firearms were dispatched to the scene to collect evidence and investigate.
Investigators haven't released any more information, but they say no arrests have been made.
Dyer was taken to Memorial Medical Center in Neillsville, where he underwent emergency surgery.
A nurse at the hospital says Dyer is in stable condition Thursday night.
Humboldt also was treated at the hospital and released.