Likely voters split 47 percent between the two major candidates, results of the poll released Monday indicated.
Romney led Obama 49 percent to 44 percent among respondents who said they would vote on Election Day, while Obama led 48 percent to 44 percent among those planning to vote before Nov. 6, the poll said.
Obama swamped Romney 54 percent to 41 percent among voters who said they already cast ballots.
"All roads to 1600 Pennsylvania Avenue lead through Ohio," said David Paleologos, director of the Suffolk University Political Research Center in Boston. "Timing is everything. Barack Obama has banked an early lead, but Mitt Romney should even the score with his slight edge among likely voters who plan to cast ballots on Election Day.
However, failure to turn out his voters on November sixth could be costly for Romney."
Libertarian candidate Gary Johnson, independent candidate Richard Duncan, and Green Party nominee Jill Stein each received 1 percent, the poll said. Three percent of likely voters asked said they were undecided.
Results are based on a statewide phone survey of 600 likely Ohio voters conducted Thursday through Sunday. The margin of error is 4 percentage points.