Yes bananas do count as 5 a day.
Bananas are very healthy and you can and should eat them at least everyday or every other day.
Bananas contain potassium as well as many vitamins, minerals and nutrients to keep you healthy and give you energy.
Other fruits that count as your 5 a day are bananas, pears, apples, canned fruit, 2 plums, 2 satsumas, 2 kiwi fruit, 3 apricots, 6 lychees, 7 strawberries or 14 cherries.
Basically as long as you eat any fruits then you will be eating towards your 5 a day goal.
All fruits are healthy for you so as long as you eat fruit daily or at least eat fruits most of the time you should be okay.
I eat at least a few types of fruits per day although I do not follow my 5 a day rule when it comes to eating fruit I just eat fruit when I feel like it.