Air carrier First Officer reported discovering undeclared hazmat cargo during preflight that was for another flight. The hazmat was unloaded.

Narrative

After landing in ZZZ; I was performing the preflight walkaround. I observed seven boxes of radioactive labeled freight on the belt loader and saw the Ramp Lead and Ramp Agent having a discussion. I asked the agents if that freight was going to be loaded on Aircraft X; having not seen a hazmat declaration while initializing the box. They responded no; and said that the freight was labeled to go to ZZZ1 and they did not have a flight to ZZZ1 from ZZZ. I resumed my preflight duties and after brief consideration of the conversation I went back to verify where the freight had come from. I was told the freight had been unloaded from our flight. The hazmat was not declared for the flight. On further inspection the baggage tag was for Aircraft Y; ZZZ2 to ZZZ1. The ramp agents explained that they were in phone communication with Company freight department and the freight would not be reloaded on Aircraft X. I thanked them and resumed the preflight of the aircraft. I explained what had happened to the Captain. The Captain communicated with Load Planning and we were assured that the freight was not reloaded on Aircraft X. The flight operated safely without further incident.