Air Carrier Captain reported ramp agent came into view from under nose area of aircraft after plane had taxied to a ramp departure location. Captain was unaware agent had approached aircraft to secure an access door that was left open.

Narrative

At XA55z ground crew could have gotten injured due to their actions. We pushed back from the gate. Received a waive off; taxied out to spot 10 with ramp control. Switched to metering per ramps instruction. Switched to ground per metering instruction. Ground told us to taxi via west 1. We cleared the area left; right and ahead; released the parking brake and added a small amount of thrust to star taxi. Right then a ramp personal walked backwards from under the nose (not visible before doing so) and held up an X. I pressed the brakes and highly doubt the aircraft had moved more than an inch from where I released the parking brake. Simultaneously with these actions; ground said hold position it appears ramp personnel are back at your aircraft. We switched to ramp and we were told a panel was open so they had come back out to close it. This was the first time we were made aware people would be approaching the aircraft. Ramp closed the panel and left without giving us a waive off. We asked ramp if the ramp personnel were clear; he was unsure. We asked ops to confirm personnel were clear. He sent out another ramp person to give us a waive off. Taxied out without ant further incidents.