A study among more than 2,600 adults by Legal & General found that confidence levels had fallen by 6% to 72%.
The report, published ahead of new unemployment figures tomorrow, also showed that 25 to 34-year-olds were most confident about their job.
Almost one in five workers said they worried about how they will maintain their current standard of living over the next three months.
Mark Holweger, director of Legal & General's general insurance business, said: "Our job security index paints a very different picture from a year ago, with confidence in job security falling from its highest level in October 2012 to its lowest level today.
"However, it's interesting that this low level of confidence in job security appears to be in conflict with the most recent labour market statistics, which show that the unemployment rate for the UK population is at a lower level than it was in October last year.