The protesters were penned into an area in Richmond Terrace, where they brandished a Confederate flag in a clear reference to the Charleston church shooting by a white supremacist last month.
An estimated 200 police officers were present to keep order - apart from some minor scuffles the demonstration appeared to pass off peacefully.
The rally had originally been planned to take place in Golders Green but police had decided it should be relocated over public safety fears.
Groups among the counter-protesters included United Against Fascism, the Green Party, the Socialist Worker Party and left-wing Jewish group Jewdas.
A spokesperson for Jewdas said: "We should oppose Nazis wherever they happen to be, to make a loud noise to show that we're opposing them in central London too - it's not just Golders Green.
"There are Jews here too. By being here at least passers-by aren't walking by and just seeing another rally, they're seeing people opposing them.
"These people don't just have crazy ideas, they have racist ideas. They hurt people, they beat up people. We stand against them."
An Israeli flag joined to a Union Jack was among the banners displayed.
One counter-protester, Amos Schonfield, a movement worker for Masorti youth group Noam, said: "I'm here because there are Nazis here. It doesn't matter if they're in Golders Green or not, we have to stand up.
"I was fully expecting the people who planned to march in Golders Green to be here. It's a shame that there are groups who believe antisemitism only matters in Golders Green, but I'm happy to see lots of people here. There are Israeli flags here - I think antisemitism and anti-Zionism are different, but if people want to counter-protest that way, that's fine."
The rally had been called as a protest against "Jewish privilege", particularly the existence of volunteer neighbourhood watch group Shomrim, which the extremists referred to as "a Jewish police force".
One extremist said: "It's not about hating the Jews, they're taking away our rights. What if the Muslims do it [start their own version of Shomrim] next?"
A police officer explained that if the rally had gone ahead in Golders Green, home to one of London's largest Jewish communities, the likely result was "serious disorder, serious disruption to the life of the community and intimidation of others.”
A small contingent of police officers was on duty at Golders Green Tube station during Saturday. They were there "just in case" any extremists attempted to protest in the area, an officer said. No incidents were reported.
Community Security Trust volunteers were also a highly visible presence on the streets of the north-west London suburb.
CST's Dave Rich told reporters: "The demonstration has been moved which we are very pleased about. We will still be having a security presence in Golders Green just in case anybody does turn up.
"We are not aware of any plans to do so but we are covering all eventualities."
The protest brings to a close a month of activism which has seen formal bodies and the Jewish community mobilise around groups like Golders Green Together and the Campaign Against Antisemitism in response to extremists' plans.
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