The Highlands and Islands MSP who discovered the move, which followed the creation of a single police force last year, is to raise the issue in Holyrood and with the Chief Constable of Police Scotland Stephen House.
John Finnie, the Independent MSP for the Highlands and Islands who was a police officer and a full-time elected official of the Scottish Police Federation (SPF), said it was a "worrying development".
Officers can be armed when keeping a watching brief on customers dispersing from night clubs in the early hours of the morning, it has emerged.
Mr Finnie, who was also a parliamentary liaison officer to Justice Secretary Kenny MacAskill until he left the SNP in 2012 in protest at the party's decision to end its long-standing opposition to Nato membership, said: "There was an armed response vehicle (ARV) in the old Northern Constabulary force area. But then the firearms were stored in locked gun-safe in the boot of the vehicle and could only be removed from the safe on the authorisation of a senior officer.
"But I am now reliably informed that, since the advent of Police Scotland, officers deployed in the ARV wear a side-arm all the time."
He said these officers were routinely deployed policing the major trunk roads and on occasion support other operational officers on non-firearm-related police business. This included supporting officers at the time when the nightclubs are closing and people disperse.
"So, you have armed uniformed officers on the streets of the Highlands for what is routine police business of monitoring crowds leaving licensed premises," he said.
He added that given his background in the police and the federation, he recognised and accepted the need for a risk assessment of every situation. However, he could not understand how any meaningful assessment could identify a routine need for guns.
"I understand this is uniform practice across Scotland. But the routine deployment of armed officers in the Highlands, even in small numbers, is a very worrying development."
He said he was dismayed at Police Scotland's failure to recognise the unique nature of policing in the Highlands and Islands.
"I will write the chief constable reminding him the Highlands and Islands is the safest place in UK because of public support - and co-operation could be threatened by police appearing militarised and unapproachable. I also intend raising this matter at the Parliament's Police Committee."
When asked whether officers could be wearing side-arms while supervising the departure of late-night revellers, Chief Inspector Charles Armstrong said: "All officers within specialist services, which includes armed policing, are deployed in support of their colleagues in territorial divisions.
"They have their part to play in keeping people safe and that includes addressing concerns within communities and responding to calls. I can confirm armed-response officers within Police Scotland are routinely armed and have been since April 1, 2013."
Police Scotland was criticised when it cracked down on saunas in Edinburgh that sold sex.
The practice had been tolerated for health and safety reasons under Lothians Police, but Strathclyde took a tougher approach on its patch and critics said it was this tougher policy that appeared to be adopted under the new national force.