Armed police were called to Sleaford railway station on Saturday evening after reports from a train guard that a passenger was suspected to be carrying a firerm.
A British Transport Police spokesman said officers were joined by armed units from Lincolnshire Police at 6.58pm following the reports from the guard.
Station Road was blocked by four or five police vehicles in response to the alarm call.
The spokesman said: “A 23-year-old man from Doncaster was arrested for possession of an imitation firearm. He remains in police custody where he is helping officers with their enquiries.”