Arias completed 22 of 40 passes for 292 yards for the Bengals (7-3, 5-1 Big Sky), including a 24-yarder to Madison Mangum with six minutes left, pushing the lead to 30-21. Mangum caught 10 passes for 159 yards. Xavier Finney ran for 125 and Zak Johnson kicked three field goals.
The Bengals responded with two Johnson field goals to lead 23-14.
Brown rushed for a TD from the 2 with 2:14 remaining and the Mustangs (6-4, 5-2) were within two, but Idaho State recovered the onside kick.