Updated 10:15 a.m.
The Associated Press reports that Cliven Bundy is being charged with assault and conspiracy for 2014 standoff near his Nevada ranch.
Bundy was arrested in Portland, Ore., Wednesday night.
Two of Bundy's sons, Ammon and Ryan, were arrested Jan. 27, when they left the Malheur National Wildlife Refuge outside Burns, Ore., which they had occupied since the beginning of January.
Cliven Bundy had said earlier this week that he intended to travel to Oregon to support the four men still occupying a government building on the refuge.
On Wednesday at the refuge in southern Oregon, the FBI moved to further restrict the movement of the four militants and is actively negotiating with them, Oregon Public Broadcasting reports.
The FBI said on Twitter that around 4:30 p.m. PT, one of the occupiers rode an ATV past established barriers on the refuge grounds, and sped away when authorities approached. The FBI says after the incident agents placed barricades around the occupiers' location.
The 40-day occupation near Burns, Ore., began as a protest of the imprisonment of two local ranchers, who were convicted of arson on land overseen by the Bureau of Land Management.
Authorities have taken a cautious approach in dealing with the occupiers, resulting in a lengthy standoff that led to contentious community meetings in the area, with many locals urging the group to leave.
Five of the militants, including leader Ammon Bundy, were traveling to such a meeting on Jan. 26 when authorities moved to arrest them. Robert "LaVoy" Finicum, who had acted as one of the group's spokesmen, was shot and killed in the incident.
Three other militants were also arrested that day, and several others occupying the ranch chose to leave, with four holdouts remaining.