The top military commander said America has "a very narrow window" of appropriate actions in the defiant country.
On the U.S.'s counterinsurgency strike in southern Afghanistan last week, Mullen said, "I'm comfortable with the strategy." He said the mission, which is largely focused on security for Afghanis, will include some of the "toughest fighting" the country has seen.
"It's already started out to be pretty tough. We've made some advances early. But I suspect it will be tough for a while," he said.
On Pakistan, Mullen said that country's efforts combating Taliban extremists have gone "pretty well" and mark an improvement.
In addition to saying he is "comfortable" with the defensive posture being taken against North Korea, Mullen discussed the strategy of decreasing U.S. troop strength in Iraq to guest moderator CBS News political analyst John Dickerson.
The admiral will accompany President Obama to Moscow Monday.
To watch Adm. Mullen's appearance on "Face the Nation" click on the video player below.