Coach Art Briles announced the dismissal Friday in a brief statement that offered no other details. Armstead played 27 games for the Bears, with five catches for 62 yards and one touchdown.
The decision comes two weeks after defensive end Shawn Oakman and safety Orion Stewart were suspended for the season-opening win over SMU for violating unspecified team rules. Both played last week in a victory against Lamar.
Baylor's season began shortly after the school hired an outside law firm for an independent investigation into the university's handling of sexual assault complaints, including one that led to a conviction against former transfer Sam Ukwuachu.