The Minnesota State Patrol says the 25-year-old Johnson was stopped about 2 a.m. for failing to signal a merge on an interstate ramp while driving in Minneapolis.
During the stop, the trooper noticed Johnson had bloodshot, watery eyes, slurred speech and smelled of alcohol. The state patrol says Johnson's blood-alcohol level was 0.12 percent during field sobriety tests. The legal limit in Minnesota is 0.08 percent.
Johnson was booked into the Hennepin County jail and released.
The Vikings say they're aware of the incident but declined further comment.
Johnson was a second-round draft pick in 2008 who lost his starting job this season to Jamarca Sanford. Johnson dropped what would've been a game-saving interception at the goal line in Sunday's loss to Tampa Bay.
Last month, the Vikings waived quarterback Rhett Bomar not long after he was arrested on charges of drunken driving during training camp. He did not play in the first three exhibition games.