Cooper DeJean's brother is in trouble with the law ... cause TMZ has learned Beckett DeJean was arrested for operating while intoxicated.

According to jail records, seen by TMZ, Beckett was taken into custody Sunday morning in Iowa on a first offense DUI/OWI, which is classified as a misdemeanor but still carries serious penalties.

Beckett was a defensive back for the South Dakota Coyotes, where he played as a redshirt freshman. Beckett's older brother Cooper is currently an NFL cornerback for the Philadelphia Eagles.

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We're working on more details surrounding the stop and arrest, but first offense DUI/OWI charges in Iowa can still result in serious fines, license suspension, and possible jail time.

As we reported ... Cooper's been spending time with WWE star Nikki Bella. Sources told us the two have been on dates ... but Nikki is still very single and enjoying life.

Story developing ...