A Quinnipiac University poll released Thursday found the former congressman was ahead of Specter 46 percent to 41. The poll of 1,412 voters was taken from March 30 to April 5.
Toomey trailed Specter in a poll released last month.
In the new survey, Specter was viewed unfavorably by 46 percent of voters and 17 percent of Democrats.
"On paper, Sen. Specter is vulnerable in the general election because only 36 percent of voters say he deserves another term," Peter Brown, assistant director of the Quinnipiac University Polling Institute, said in a statement. "But Toomey is so little known that the electorate is torn which way to go."
Meanwhile, Toomey also led Rep. Joe Sestak (D-Pa.), Specter's primary opponent, by a 42-34 margin in the Quinnipiac poll.
Toomey and Sestak meet in a televised debate Sunday. Toomey is expected to win the GOP nod to face either Specter or Sestak.