No problem is an English expression, used as a response to thanks (among other functions). It is regarded by some as a less gracious alternative to "you're welcome", which shares the same function. It is similar to the Australian English expression no worries. The phrase is used in most of the United States, especially on the East Coast of the United States.
Some find the expression, particularly when employed in the service industry, to be rude, implying that a reasonable request could have been received as problematic or unwelcome.
It is widely believed that younger speakers especially favor "no problem" over "you're welcome", and empirical research has corroborated this belief.
References
No problem Wikipedia(Text) CC BY-SA