Kaine, a former governor of Virginia, made the comment Thursday during a debate with Republican George Allen, another former governor and Kaine's opponent in the senatorial race, The Washing Port reported. It was their first televised debate.
After the debate, Allen said Kaine's record "is always one of looking to raise taxes. When he was governor, he tried to raise taxes on people earning as little as $17,000 a year. He wanted to raise taxes on buying used cars."
Kaine said in the debate that he would be open to "some minimum tax level for everyone." He later qualified his statement, saying he didn't actually propose a minimum income tax, the Post said.
He was responding to a question about the controversial comment Republican presidential candidate Mitt Romney made about "47 percent" of Americans not paying income taxes.
"I would be open to a proposal that has some minimum tax level for everyone but I do insist many of the 47 percent that Governor Romney was going after pay a higher percentage of their income in taxes than he does," Kaine said during the debate.
Kaine's discussions of his plan for fixing the country's fiscal problems during the debate didn't involve such a tax, the Post said.
On Wednesday, a Washington Post poll indicated Kaine had an 8 percentage point lead over Allen in what is considered to be among the most competitive races in the country.
Kaine and Allen are battling to succeed the retiring Sen. James Webb, a Democrat. Allen lost the seat to Webb six years ago.