The lead was within the 2 percentage-point margin of error.
In past elections Italian exit polls have often proved unreliable.
In the lower house, a one-vote majority would be enough to give the winning party a solid majority of seats, under Italy's election law.
Both Berlusconi, a media tycoon and two-time former prime minister and Veltroni, a former mayor of Rome, have promised to reverse Italy's economic downturn and said that Italy needs more police to tackle crime.
The early election was called after the centre-left government of Romano Prodi collapsed in January, having completed 20 months in power.
Franco Pavoncello, a politics professor at John Cabot University in Rome, said; "Let's see what happens in the Senate. If those are the numbers, I don't think we have a victor.
"Berlusconi may carry the lower house, but with the way things are structured in the upper house, Veltroni could have an alliance and control the senate. So we're stuck."
Luigi Speranza, an economist at the French bank BNP Paribas, said: "These exit poll results are so close that they don't eliminate the spectre of one chamber going to one side and the other chamber going to the other.
"That would mean more uncertainty which in the short term is the worst possible scenario for Italy's economy at a very difficult time. But the situation is very unclear and we need to wait longer to have a better picture."