"We always monitor the situation. And Chairman Un has said that there would be something over Christmas," Robert O'Brien told ABC News Chief White House Correspondent Jonathan Karl on Sunday.
"I think the president has engaged in personal diplomacy at a very high level with him over the years. And they have a good relationship personally. So perhaps he's reconsidered that. But we will have to wait and see," O’Brien added.
As for whether or not there will be consequences if North Korea does test long range missiles again, O'Brien said that the U.S. will reserve judgment and take action if necessary.
"If Kim Jong Un takes that approach, we will be extraordinarily disappointed, and we will demonstrate that disappointment," he said.
North Korea's vice minister of foreign affairs suggested in a statement earlier this month the country would give the U.S. a "Christmas gift" ahead of its year-end deadline for progress on nuclear talks. That message put officials in the U.S. and South Korea on high alert for a potential long-range missile test over the holidays.
Trump dismissed those concerns on Tuesday, joking at his Mar-a-Lago resort that the gift could be a "beautiful vase."
"Maybe it's a nice present. Maybe it's a present where he sends me a beautiful vase, as opposed to a missile test, right?" he said.
Talks between the U.S. and North Korea had stalled since negotiators last met in October.
But Trump's national security adviser said the White House believes the diplomatic process can still have success.
"Kim Jong Un promised to denuclearize the Korean peninsula and we want to hold him to that commitment and we hope he follows through with the commitment that he made in Singapore," O’Brien said.
A senior North Korean official also called Trump a "heedless and erratic old man" earlier this month after the president tweeted about the country and its leader, but on "This Week" Sunday, O'Brien said not to read too much into the slight because "actions speak louder than words."
"We'll have to see what actions the DPRK takes and Chairman Kim take," he added. "He has two paths in front of him, he's got a glorious path for the people of North Korea where they could become like South Korea and be a very prosperous, very wealthy country, or there's another path that takes them down the road of sanctions and isolation and being a pariah state. And we'll see which one they choose."
O'Brien's predecessor, John Bolton, has criticized North Korea since leaving the post. He said he didn't think North Korea would "ever voluntarily give up nuclear weapons" in a recent interview with NPR.
O'Brien told Karl that the president has a lot of respect for Bolton, but that the two don't always view diplomacy the same way.
"We've gone for a period of time without a nuclear test. We've diffused a very high tension situation, and so we're going to have to see if the president's approach works," O'Brien added.
O'Brien, who was named as Bolton's replacement in September, also responded to speculation that Trump was eyeing him as a potential replacement for Secretary of State Mike Pompeo if Pompeo decided to run for the open U.S. Senate seat in his home state of Kansas.
"I love the job I've got now, I get to work with the president every day and I'm very happy sitting where I am," O'Brien told Karl.
"I hope and I expect Secretary Pompeo will stay. I spoke with him about this two nights ago, he said he's not running for Senate. He said he's staying as Secretary of State and this is one American that's very pleased that the president picked Mike."