Do we really need an antivirus app for our mobiles?

As the title shows, do we really need an antivirus app installed on smartphones to keep us safe? Why? Is there any virus on Android OS?

I'm nt sure bt I think if we r online through mobile, virus cn hack our mobile. Tht's why, we need antivirus on our android phone bt I don't know why we need antivirus on android based whn we r offline I mean don't use internet on phone

To me, smartphone is just like a mini computer, I use it for Internet surfing a lot. So, I guess I need to have an antivirus app installed on it.