The latest Rasmussen Reports survey shows Burr with the support of 54 percent of likely voters, with Marshall backed by 38 percent of likely voters and 1 percent favoring some other candidate. Seven percent were undecided.
Last month, the Rasmussen Reports poll showed Burr leading Marshall by a 49-40 margin, reports Rob Christensen.
Rasmussen has shown Burr with a lead for most of the year except for shortly after the June Democratic primary, when Marshall's victory gave her a temporary bump, allowing her to pull even with Burr.
The survey of 500 likely voters was conducted on Sept. 8 by Pulse Opinion Research with a margin of error of plus or minus 4.5 percentage points.
Burr's first TV ad had been airing a week when the poll was taken, while Marshall has yet to begin her advertising.
If there is any good news in the poll for Marshall – and there doesn't seem to be much – it is that her supporters seem more committed to voting for her.
The poll also found that 57 percent of North Carolina voters favor repeal of the new national health care law, while 35 percent oppose repeal. Burr opposed passage of the health care bill and favors its repeal, while Marshall was a supporter of the health care overhaul.
Seventy-one percent of North Carolina voters say the country is still in a recession and say the economy is the top issue.
Forty-four percent approve of the job that Democratic Gov. Bev Perdue is doing, while 54 percent disapprove.
UPDATE: The Marshall campaign dismissed the poll results.
"This is a right-leaning pollster, and an outlier poll at that," said Sam Swartz, Marshall's spokesman.
"After 16 years in Washington, public polling has consistently shown that North Carolina voters don't like the job Senator Burr's doing, and that Elaine Marshall is within striking distance."