Larry Mitchell Hopkins, 69, is a member of an armed group that reportedly arrested migrants near Sunland Park, New Mexico, Attorney General Hector Balderas said in a statement.
Hopkins – also known as Johnny Horton Jr. – was arrested on alleged charges of possession of firearms and ammunition, according to a statement by the FBI field office in Albuquerque.
Earlier this week, videos were posted online allegedly detaining migrants by a militia known as the United Constitutional Patriots before being handed over to the US Border Patrol.
"This is a dangerous offender who should not have weapons near children and families," Balderas said. "Today's arrest by the FBI clearly shows that the rule of law should be in the hands of trained law enforcement officers, not armed civic militants."
Hopkins is expected to appear in court for the first time on Monday, the FBI said. CNN was unable to determine on Saturday whether he was represented by a lawyer.
CNN has commented on the United Constitutional Patriots, but has heard nothing.
Videos show armed men in masks, fatigue
Various private militia groups, which often demand anti-immigrant views, have patrolled the border for years, but footage of an armed group holding migrants is rarely on the US side of the border.
Detention group imprisoning migrants, including families with children who have just crossed the border.
CNN has contacted the group and the people who posted the video for comment but did not confirm any details about it who took the videos or when and where they were shot.
In the footage, people wear full military fatigue Man can see them with handguns attached to the sides wearing gloves and black face masks. Armed men order the migrants to stop, force them to sit on the ground and appear to call the border patrol to pick up the migrants.
In at least two videos posted on the group's Facebook page, a man with fatigue verbally identifies himself as a "Border Patrol" if he detains a group of migrants.
An US Customs and Border Guard refused to comment on the United Constitutional Patriots and online videos, but said that the agency "neither private groups of organizations that take enforcement action into their own hands still approve of it. "
CNN's Catherine Shoichet, Rebekah Riess, Deanna Hackney, Geneva Sands and Paul P. Murphy contributed to the report.