Alex Salmond's party has the support of 38% of voters compared with 35% for Labour across Scottish constituencies, the YouGov survey for The Times newspaper shows.
The results extend the SNP's lead over its rivals by one point in a month.
For regional voting, Labour has slipped two points to an equal position with the SNP on 33%.
Meanwhile, support for the Liberal Democrats has increased from 5% to 7% on both votes, while backing for the Conservatives fell from 14% to 13% in constituencies and regions.
The Green vote increased by one point to 7% in regions.
The results are based on responses from 1,072 Scottish adults between March 20 and 24.