He was stopped at a local intersection for not having his headlamps illuminated, Detective Sgt. Travis Welsh said.
An investigation began and culminated in the driver's arrest for DUI, which was a misdemeanor charge.
Johnson was cooperative throughout the incident and was in the car alone. He was offered a breath test which he refused, but Johnson was deemed intoxicated based on the totality of circumstances in the investigation.
The former University of Montana standout posted a $700 bond, according to The Associated Press.
The Rams released a statement regarding the matter that read, "We are aware of the situation regarding Trumaine Johnson. We are gathering more information and will have no further comment at this time."
This isn't the first run-in with the law for Johnson. While at Montana, he was arrested and tasered by police in October 2011. In Missoula Municipal Court, Johnson and a teammate pleaded no contest to misdemeanor disorderly conduct charges in connection with the incident, according to the Billings Gazette.