Passengers were evacuated from the city station at around 3pm on Tuesday, forcing trains - including those heading to and from Shrewsbury and Telford - to be cancelled or delayed.
British Transport Police has now confirmed a man has been arrested.
A spokesperson said: "A statement from British Transport Police said: "Officers were called to Wolverhampton railway station at 2.56pm yesterday (May 10) following reports of a man in possession of a firearm.
"Specialist officers attended, and a man was arrested on suspicion of possessing a firearm in a public place and conveyed to police custody where he remains.
"An imitation gun was recovered from the man’s bag."
Witnesses at the scene described how they were told to quickly evacuate from the station.
Ben Holleron, 36, from Wolverhampton, said: "It all happened so quick. My train was about to pull in to go to Manchester.
"We were on platform two and the police asked us to evacuate platform two," he said, before saying he heard officers say "get everybody off now".
"They kicked everybody out the station at that point," he added.
A man who did not want to be named, was stuck on a train from Birmingham to Wolverhampton. He said: "I was travelling from Birmingham, and we stopped outside of Wolverhampton.
"We were waiting on the train for around 25-30 minutes.
"We were informed that there was a police incident going on, and that's all we were told."
A group of friends said: "We did not see exactly what was going on but we saw police officers running around the platforms, and were told to evacuate quickly because of an incident."
A West Midlands Railway spokesperson said: “Passengers were asked to leave Wolverhampton station for a short time on Tuesday afternoon while the police attended following a report of a person acting suspiciously.
“The station was fully reopened at around 3.30pm and services are now running as usual. Any passenger whose journey was delayed by 15 minutes or more as a result of the incident can claim compensation via Delay Repay.”