(That is) not a problem; I don't mind; don't worry about it. A: "It looks like the file was deleted when the computer crashed. I'm so sorry!" B: "It's no trouble. I always make a backup copy at the end of the day." A: "Sorry about last night, I was out of line." B: "No trouble, man. I know you didn't mean it."
(It's) no trouble (at all).
Do not worry, this is not a problem. Mary: Do you mind carrying all this up to my apartment? Tom: It's no trouble. Bob: Would it be possible for you to get this back to me today? Bill: Sure. No trouble at all.