B737-800 First Officer reported a ramp agent approached the aircraft and opened a panel door while the aircraft was still parking at the ramp with engines running.

Narrative

Upon taxiing into our gate at ZZZ last night; with the aircraft still moving and approximately 20-25 feet until STOP on the DGS (docking guidance system); I noticed out my right window one of the ground service agents walking towards the aircraft. The agent disappeared under my window out of my sight. Within seconds I could clearly hear what sounded like the unlatching and opening of the ground power and interphone service panel door. The Captain was taxiing the airplane very slowly into the gate; however the aircraft was still moving. Given recent events of ground personnel injuries and even deaths on the ramp while the aircraft was still moving with engines running; I thought that was a major lapse in judgement on the ground agents part. The agent seemed to have done this before based on body language and the continued noises I heard on the ground service panel. Furthermore; this agent could have easily tripped and fell and the nosewheel rolled over him; or worse they could have been ingested into the #2 engine. Typically I notice Captains have minimal power applied to the engines while taxiing in so they don't have to spool the engines just in case they stop a few feet short of the parking line. It is my understanding that ground agents are to wait until the engines are shut down and beacon turned OFF until opening of any doors/compartments.Emphasize during initial and follow up training to not approach the aircraft while it is moving no matter how slow until it comes to a complete stop.