Anger is an important emotion to feel. It alerts you to the fact that you’re feeling provoked or wronged in some way. Thus, it’s bad to deny that you’re angry. Telling yourself or others you are “fine” only minimizes whatever the problem is that caused the anger in the first place.
What should you do instead? Be honest with yourself and reflect on what is causing the anger. Admit to yourself that you are mad, think about why you are mad, think about the consequences of acting on that anger, and try and address the issue. This is all part of what it means to be emotionally intelligent.