Love was in the air, and on the field, at Lucas Oil Stadium ... an Indianapolis Colts' cheerleader got engaged after her boyfriend proposed right on the turf during one of the squad's performances!

The cute moment went down on Sunday in Indy during the Colts' Week 6 showdown against the Arizona Cardinals. Instagram/@coltscheer

As the Colts cheerleading team was mid-routine, performing near the endzone in the second half, a man wearing a "Marry Me" custom Colts jersey snuck up behind Mika.

Completely unaware her BF, Spencer , was behind her, Mika kept dancing ... until she finally turned around and saw him down on one knee!

Mika -- who's been an NFL cheerleader for four years -- immediately got emotional and kissed her man before putting the massive diamond on her ring finger.

He

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