However, as of Wednesday night the Chiefs still hadn't signed first-round selection Eric Berry, a safety who is expected to become an instant starter.
Terms of the contracts for McCluster and Arenas weren't released.
The 5-foot-8, 170-pound McCluster caught 130 passes for 1,703 yards and seven touchdowns for Mississippi.
Arenas had 154 tackles and six interceptions in 52 games for Alabama.
The Chiefs also signed 6-foot-3 tight end Leroy Banks, who was awarded to Kansas City via a waiver claim. Banks entered the NFL as a rookie free agent with Atlanta and played 23 games in two seasons at Southern Mississippi, catching 34 passes for 462 yards and four touchdowns.