Romney bagged 47 percent of the vote and Obama had 45 percent on the survey taken last week among registered U.S. voters.
The previous Gallup survey conducted in late March had the president with 49 percent and Romney, the presumptive Republican nominee, with 45 percent.
The results were also highly partisan with both Obama and Romney supported by 90 percent of the registered members of their respective parties. Respondents identified as independents leaned strongly toward Romney, with 45 percent compared to 39 percent for Obama.
Gallup noted the poll was conducted Wednesday through Sunday, after Rick Santorum dropped out of the GOP race. It surveyed 2,265 registered voters by telephone and carried a margin of sampling error of 3 percentage points.