A man and woman were threatened with a gun and knife by a man who demanded their car keys.
Police were called to Haven Road in Fazakerley on Saturday morning to reports the pair had been threatened in the street.
The man, who was said to have a gun and knife, reportedly demanded the keys to their car but they refused.
A short time later, he is believed to have threatened staff with a knife at a nearby shop.
A man was arrested by armed officers nearby on Longmoor Lane and has been taken into custody for questioning.
A spokesperson from Merseyside Police said: "Armed officers have arrested a man in Fazakerley this morning following reports of a man armed with a gun and a knife making threats.
"Officers were called to Haven Road, Fazakerley, just before 9am after reports that a man had threatened a man and woman with a gun and a knife and demanded the keys to their vehicle.
"They refused and the man left. It is also believed that the man threatened staff with a knife at a nearby shop just after this incident.
"Armed officers responded to the calls and a male was arrested nearby on Longmoor Lane.
"He was found to be in possession of an imitation firearm and a knife was also found nearby.
"The man was arrested on suspicion of possession of an imitation firearm, possession of a knife and attempted robbery.
"He has been taken to a police station where he will be interviewed by detectives."