In the absence of any other information, I'll assume that you're using an Android device.
There are plenty of security companies who would like you to believe that you need their products in order to keep your phone (or tablet or whatever) secure. However the risks are far lower with the Android operating system than with Windows. That's because apps are 'sandboxed' so that something dodgy with one of them can't affect one of the others. (Well, that's the theory anyway!).
This page covers it all quite well. (Avast Mobile Security is mentioned there and is extremely popular):
http://www.digitaltrends.com/mobile/top-android-security-apps/
However, as with Windows, some basic common sense is at least as important as using any security software, as explained here:
http://www.digitaltrends.com/mobile/android-app-security-basics/