The National Front leader was seen having coffee at Trump Ice Cream Parlor on the ground floor of Trump Tower, with three men including her partner Louis Aliot, the party's vice president.
Also sighted with Le Pen was George "Guido" Lombardi, an Italian businessman who lives in Trump Tower and was described in a Politico profile as Trump's "self-professed contact to Europe's far-right parties."
Asked by journalists if she was there to meet Trump, Le Pen refused to respond.
"She is not meeting with anyone from our team," Trump spokeswoman Hope Hicks told reporters.
Earlier, Trump spokesman Sean Spicer said curtly: "No meetings. It's a public building."
Le Pen's campaign manager, David Rachline, had said earlier in Paris that Le Pen was on a "private" visit to New York and would not be meeting with the future US president.
In November, Le Pen -- who describes herself as "anti-establishment," rejecting the politics of both right and left -- was among the first foreign politicians to congratulate Trump on his surprise election victory.
And she saluted Trump after he said he had persuaded American automaker Ford to produce a certain model in the United States rather than Mexico, though Ford said its decision was based purely on business considerations.
Opinion polls in France predict that Le Pen, an unsuccessful presidential candidate in 2012, will make it to the second round of French elections in May to determine a successor to socialist President Francois Hollande.
Trump Tower, in an area with many popular shops, remains accessible to the public, though stringent security measures have been put in place since his election on November 8.
