Error while building Razor template - The type or namespace name 'Web' does not exist

I am using Razor Template in Xamarin Studio for building a hybrid application, but while compiling, I am getting a strange error like this

Error CS0234: The type or namespace name 'Web' does not exist in the namespace 'System' (are you missing an assembly reference?) (CS0234) (HybridHelloWorld)

Xamarian Studio ver : 4.2.5 Xamarin.Android Version: 4.12.3 (Starter Edition)

Please help.