The poll of almost 13,000 UK employees shows that, on average, public sector staff had taken nearly three days off sick in the last year because of problems with their mental health, compared with less than one day on average for workers in the private sector.
Forty-eight per cent of the public sector workforce reported taking time off work due to mental health issues, while less than a third (32%) of workers in the private sector did the same.
More than 5.4 million people are employed by the UK's public sector, almost 3 million of whom are employed by central government. Fifteen per cent of these reported having poor mental health compared with 9% of private sector staff, Mind found.
The public sector as a whole was more aware of the issue of mental ill-health in the workplace than the private sector, the results of the survey indicated.
It found that public sector staff were more likely to tell someone if they had a mental health problem. They were also more likely to be honest if they took time off work due to this reason.
Of the survey respondents with a mental health condition, 90% of the public sector workforce told their employers, compared with 80% of those in the private sector. When taking time off for mental health reasons, 69% of public sector and 59% of private sector workers said they were honest about the reason why.
However, workplace mental health support was found to be lacking for those in the public sector. Less than half (49%) of people said they felt supported when they spoke up about mental health problems, compared with 61% in the private sector.
Paul Farmer, chief executive of Mind, said: "A vital part of changing the lives of people with mental health problems is to tackle the culture of fear and silence in the workplace that stops people opening up about what they are experiencing.
"This data shows that the public sector in particular is making progress here. But it's also vital that when people do speak out they get the right help and support at the right time. It's clear there is still a long way to go in both the public and private sector to address the gap between people asking for support and actually getting what they need.
"By promoting wellbeing for all staff, tackling the causes of work-related mental health problems and supporting staff who are experiencing mental health problems, organisations can help keep people at work and create mentally healthy workplaces where people are supported to perform at their best."
The results are based on Mind's online survey of 15,022 employees, of which 5,746 worked in the public sector and 7,191 worked in the private sector. The remainder worked in the third sector.