NBC said the survey raises the possibility that Santorum was building momentum among GOP voters after his strong showing in Michigan, which was considered by analysts to be a Romney stronghold. But pollsters said it was too early to predict a winner.
"I just think it's going to very close," said Lee Miringoff, director of the Marist College Institute for Public Opinion.
The survey also found Santorum getting higher marks for his conservatism and connection with the middle class, but Romney leading among voters who consider him the best candidate to defeat President Obama in November.
Romney had the lead in Virginia, another Super Tuesday state, in a separate NBC/Marist poll. Romney was favored by 69 percent of likely voters. Ron Paul, the only other candidate on the ballot, had 26 percent.
The Ohio poll was conducted Feb. 29-March 2, surveyed 3,079 registered voters and had a margin of error of plus-minus 1.8 percentage points.