The arrest was the first made since the group took over buildings at the Malheur National Wildlife Refuge on Jan. 2 in the latest conflict over the U.S. government's control of land in the West.
Law enforcement officials had so far kept their distance from the site, located about 30 miles south of the small town of Burns in Oregon's rural southeast, in an effort to avoid a violent confrontation.
But police arrested Kenneth Medenbach, a 62-year-old resident of Crescent, Oregon, after he drove a vehicle owned by the U.S. Fish and Wildlife Service to a local supermarket on Friday, the Harney County Sheriff's office said in a statement.
He was charged with unauthorized use of a motor vehicle. Medenbach could not be reached for immediate comment and it was unclear if he had retained an attorney.
The group, led by the sons of a Nevada rancher who with a large group of heavily armed men successfully stared down federal agents in a 2014 dispute over grazing fees, had earlier made a public call for help with supplies to cope with the winter weather, with temperatures at the reserve expected to dip below freezing in the coming days.
That plea led to shipments of sex toys, glitter and nail polish, which prompted online video complaints by the occupiers.
The occupiers declared their move a show of support for two local ranchers, Dwight Hammond Jr. and his son Steven, who were returned to prison earlier this month for setting fires that spread to federal land.
A lawyer for Hammond family has said that the occupiers do not speak for the family.
Residents have expressed a mixture of sympathy for the Hammond family, suspicion of the federal government's motives and frustration with the occupation.
The chair of a local Native American tribe called on federal officials to remove the occupiers.
"Armed protesters don't belong here," said Charlotte Rodrique, chair of the Burns Paiute Tribe in a Friday statement. "They should be held accountable."