I walked into the kitchen and noticed that the gas stove was on. The last time it was used was 2 days ago and no one has touched it since. I need to know if this is dangerous and what to do?

If the burner was on , meaning with a flame, no problem except gas usage. Some people heat their house this way. If the gas valve was open without a flame, You would have smelled it. That would be more critical. They don't turn on by themselves, so watch out next time.

Yes it is dangerous. So please be careful to not letting any spark inside your house. And please be aware and always check on your gas stove everyday.