Border Patrol Spokesman Omar Zamora told the Associated Press that agents were pursuing a group of immigrants when one agent spotted a man holding a gun near the Rio Grande.
The agent fired four shots but did not hit the man, Zamora said. The man then dropped his weapon and identified himself as a militia member.
The unidentified man was not arrested and appeared to have permission to be on private property where the incident occurred, Cameron County Sheriff Omar Lucio told the AP. Lucio, whose agency is involved in investigating the incident, said the man was wearing camouflage and was carrying either a rifle or shotgun.
The sheriff said militias really aren't needed at the Texas-Mexico border given the number of law enforcement agencies already working to secure the area.
"It just creates a problem from my point of view, because we don't know who they are," Lucio told the AP.
U.S. Customs and Border Protection has said it does not "endorse or support any private group or organization from taking matters into their own hands as it could have disastrous personal and public safety consequences."