With less than a week left before the Nov. 5 general election, the Massachusetts governor’s race is a dead heat, according to a poll released Monday night by the Institute of Politics (IOP) and New England Cable News (NECN).

In a survey of 400 likely voters, Democrat Shannon P. O’Brien led Republican W. Mitt Romney 41 percent to 39 percent with eight percent undecided. The poll, conducted Oct. 24-27, has a 4.9 percent margin of error.

A Boston Herald poll released yesterday shows O’Brien leading Romney 44 percent to 38 percent, with 12 percent undecided.

“A lot of voters are going to be deciding in the next week, which often happens in these races,” said Dan Glickman, director of the IOP.

Glickman said get-out-the-vote efforts will be important for both campaigns, given the close nature of the race.

Green Party candidate Jill E. Stein ’73 received five percent in the poll, while both Libertarian Carla A. Howell and independent Barbara Johnson took three percent.

James M. Glaser, a political science professor at Tufts, said he expects the support for Stein to fade in the final week.

“The wasted vote issue comes up a bit when you have a race this close,” he said. “And that helps Shannon O’Brien.”

IOP/NECN conducted a poll Oct. 2-3, which showed O’Brien and Romney tied at 40 percent.

Since that poll, both candidates have seen a decline in the percent of surveyed voters with favorable opinions of them.

O’Brien’s favorability rating dropped from 61 percent in the first poll to 48 percent in the latest, while Romney’s rating dropped from 57 percent to 48 percent.

Glickman attributed the drop for both candidates to the contentious tone of the campaign.

“The amount of negative advertising here is significant,” he said. “It’s pulling both candidates down.”

He said the result would likely be lower voter turnout.

Paul E. Peterson, Shattuck professor of government, said this decline is normal for candidates in a competitive race.