According to data obtained under Freedom of Information request to all health boards, a total of 254,390 days of staff time were lost due to mental ill health in the first seven months of the crisis.
The greatest number of mental health absence days were taken in NHS Greater Glasgow and Clyde and NHS Lothian, the two largest health board areas.
Just 89 days were taken in NHS Western Isles and 107 in NHS Orkney.
Liberal Democrat health spokesperson Alex Cole-Hamilton said the figures showed the toll the pandemic had taken on NHS workers.
"Day after day staff have gone above and beyond the call of duty, putting their own lives at extra risk to care for others,” he said.
"These figures are an insight into the toll that mental ill health has taken over the last year, but the pressure was there before the virus struck.”
Ahead of the Holyrood election this week, Mr Cole-Hamilton outlined plans to focus on mental health recovery.
"Scottish Liberal Democrats have been constructive throughout the pandemic,” he said.
“Now we are proposing an NHS recovery plan and greater priority for mental health, including a mental health first aider in every workplace.”
Mr Cole-Hamilton added: “We want the next Parliament to have a needle-sharp focus on the recovery, the NHS and mental health. We owe it to hard-working staff, all those waiting for operations and the thousands of adults and children waiting over a year for mental health help."
It comes after new figures revealed waiting times of over two years for child and adolescent mental health services, with at least one child waiting more than three years.
An SNP spokesperson said the party manifesto has pledged to increase direct investment in mental health by at least 25 per cent, with 10 per cent of the frontline NHS budget invested in mental health services by the end of the parliament, and 1 per cent directed to child and adolescent mental health services.