ASP.NET is not a language in itself rather a web technology that uses .NET programming languages to build dynamic web sites and web applications. I suppose the question is if .NET is platform-independent?
My answer would be ‘currently,no’. .NET is slowly catching up but it is still way to go before it become platform independent. The framework works only on WINDOWS at present and not on other OS. I would say it is language independent. That is to say any language targeting CLR can be used to write code for applications.
A new project called MONO is in works which will allow the .NET framework to be installed on LINUX but there’s no official support from MS on this as of now.