You cannot execute a class file.
You cannot execute an ASP.NET page in command prompt.

The only way you could "execute" a class file in Command Prompt, you'd have to write a console application that includes your class file as a reference, and uses the class in the file.

Similarly, if you have a code-behind file with your ASP.NET page, you could copy the contents of that file into a class file, and with some minor modifications, you could probably perform the same technique.