The Labour leader said Alex Sobel a member of his shadow ministerial team and MP for Leeds North West, "knows what he said was wrong".
Sir Keir stressed that under his leadership, Labour was "very clearly pro-business". Mr Sobel's comments, made to a podcast, were reported by The Sun.
He said: "When I first became an MP, I was like, I am not taking meetings with any of these people. These people are the enemy, you know.
"I'm a socialist, my job is to effectively transform society so that we have a much more mixed economy and we don't have huge global corporations which have all this power."
Although "that is still my dream" there was not "enough time to do that and save the climate".
Sir Keir, on a campaign visit to Hartlepool ahead of the May 6 by-election, told reporters "Alex Sobel knows what he said was wrong. He has apologised. He's apologised to me.
"The Labour Party, under my leadership, is very clearly pro-business. We want a partnership with business. And Alex Sobel understands that."
Sir Keir was at Hartlepool's nuclear power station, run by energy giant EDF, which he said was "a business that provides the best part of 700 well-paid skilled jobs in the local community".
The Labour leader also faced questions about the selection of doctor and former MP Paul Williams as the party's candidate for the seat after he was the only person on the shortlist.
He told ITV Tyne Tees: "The local party were very clear that they wanted Dr Paul Williams and they were clear why, because here we have got a man who worked on the front line in the NHS over the period of the last year during the pandemic."
The Hartlepool by-election will be a key test of Sir Keir's leadership. Dr Williams will be taking on the Tory candidate, North Yorkshire farmer Jill Mortimer, as well former Labour Colne Valley MP Thelma Walker who is now representing the Northern Independence Party.The May 6 contest will give an indication of whether the Labour leader can shore up support in the party's former industrial heartlands after large sections of the so-called "red wall" crumbled in the 2019 general election.
Hartlepool is a seat long held by Labour and the party fought off a strong Conservative and Brexit Party challenge at the 2019 general election, although their majority was reduced to just under 3,600, down from 7,650 in 2017.
The contest takes place on the same day as local elections across England and votes for the Welsh and Scottish parliaments.