The AT&T-exclusive Samsung Galaxy S6 active has started receiving a new update. The update carries a build number of G890AUCS6DQE1, weighs 15.6MB, and brings along Android security fixes for the month of May.
Going by the official change-log, nothing else is included in the update. As is usually the case with OTA roll outs, it may take sometime for the update to hit your device. You can manually check for the update by heading to your phone's Settings menu.