Usually happens when it boots up, and in those cases usually because of the power save button sticking a bit, I believe there is no way to get out of download mode without rebooting, or of course loading firmware as that is the point of Download mode.
If it were my machine I would shut it down, make sure there are no USB keys plugged into it, tap the energy saver a few times (Can't hurt to tap all the physical buttons a few times just to be sure) and power it back up.
If that fails to stop it from happening, get a tech onsite and have him wipe the device and reload the firmware.
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