The first sentence is correct, but I have never heard anyone say it like that before. So, the second sentence is the way you want to say it. But you can also say "I'm in a good mood", and that would be the more common to say it....... There is also a common expression in the USA that we say. We say "I feel good today", meaning you have alot of energy and a very positive attitude today, so you are in a very good mood..... And sometime we say " I feel good" when we drink alot of alcohol (beer/liquor) and are getting a very good buzz. A "good buzz" means you are getting drunk, but you are feeling very good from drinking alcohol, so you don't usually admit it. I think "buzz" is just a slang word though, and kind of like a single word of expression. Hope that helps you understand the language a little bit better. Good luck

Both are correct. You'd usually hear ''I'm in a good mood.''

It would be "I am in a good mood" since you are speaking about how YOU are feeling it will be "am" instead of "have". "Have" would be used if you are speaking about yourself but in the sense of owning something. Example: I have a red car, I have a laptop Hope this helps!