"For us, it's a practical matter," Mattis told reporters, noting that the Olympics are South Korea's biggest event in terms of international tourism.
"We have at times changed the timelines on these (drills) for any number of reasons, so for us, this is the normal give and take that we have," he added.
He added that the drills would be conducted sometime after the Paralympics, which end on March 18.
On Wednesday, the two Koreas restored a cross-border hotline that had been shut down since 2016.
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They also agreed to hold high-level talks next week -- the first since 2015 -- which will focus on "matters of mutual interest," including the North's participation in the Winter Olympics.
Mattis said the talks were the result of international pressure, pointing to successive United Nations Security Council votes against the North.
The Pentagon chief declined to address a recent tweet from President Donald Trump, who said Washington had a nuclear button that was "much bigger and more powerful" than North Korean leader Kim Jong-Un's.
"My job as the secretary of defense is to make certain that we have forces ready to defend this country," Mattis said.