Do we really need an antivirus app on android?

It's quite confusing, That do we really need an antivirus on android?

  
If yes,why and which app?

There are some antivirus apps to have nice anti theft features and having firewall to block malicious websites that are suspicious. Provides call/sms blockers. To know which apps are using network, wifi, GPS etc through privacy advisers.

It is not necessary to use a antivirus, if you are curious than use avast antivirus,It is Free Mobile Security and it's anti-theft is best.There are other apps that offer the same.

A german security company ran a test of some anti-virus apps, There were 172 possible hits and 10 real time hits and the results were depressing:

Antivirus Free fra Creative Apps – 0/172, 0/10
GuardX Antivirus fra QStar – 0/172, 0/10
LabMSF Antivirus beta fra LabMSF – 0/172, 0/10
Privateer Lite fra Privateer Labs – 0/172, 1/10
Bluepoint antivirus Free fra BluePoint Security – 2/172, 1/10
Kinetoo Malware Scan av CPU Media SARL – 11/172, 1/10
Zoner AntiVirus Free av ZONER – 55/172, 8/10

If no.. Why???

As long as your careful then your fine no need of antivirus. Just don't download garbage blindly.
Just do not download random apk's from the internet and blindly install them.
And mainly antivirus just drain battery faster and use a lot of ram.. , your device will become Laggy.