A total of 56% of respondents to a YouGov survey for the Times said they would vote No in a future independence referendum, with 44% voting Yes.
The figures, which remove people who responded "don't know", that they would not vote, or skipped the question, show a marginal move to the No side from the 2014 referendum result of 55% No and 45% Yes.
When the YouGov poll was last carried out for the Times in September, 49% of respondents said they would vote in favour of independence while 51% would vote against.
Despite the dip in support for Scotland leaving the UK, the same poll indicated that the SNP is on course to add 11 MPs at next week's General Election.
It put the SNP on 44%, up one point on polling in August, while the Tories were on 28% (plus 8), the Liberal Democrats were on 12 (no change) and the Greens on 1% (minus 3).
According to projections by polling expert Sir John Curtice, this would see the number of SNP MPs increase from 35 to 46.
The survey also found that the number of people who believe there should be a Scottish independence referendum within the next five years has fallen.
A total of 42% of respondents were in favour, down from 45% in August, with 48% against - up from 44% in August.
More people thought Boris Johnson remaining Prime Minister next week, rather than Jeremy Corbyn taking the role, would make independence more likely within the next decade.
More than a third (37%) of respondents said Mr Johnson staying in post would make Indyref2 more likely in this timeframe, with a quarter (25%) saying it would be less likely.
For the Labour leader, 32% said him becoming prime minister would make Scottish independence more likely within the next 10 years, with 16% believing the opposite.
Pamela Nash, chief executive of Scotland in Union, said: "This is yet another encouraging poll which shows that a majority of people in Scotland want to remain in the UK."
She added: "Voters are being turned off by the Nationalists' negative inward-looking vision for Scotland."
The poll surveyed 1,002 Scottish adults from December 3 to December 6.