Because the programs written in C# require components of the .NET framework, it is impossible to run a C#.NET program without it. The source code you write doesn't get compiled directly into any kind of low-level language, but into an intermediate language that must talk to the .NET framework.
As it's been said, you can always include the framework as part of your program's distribution. Otherwise, anyone can download it FREE from Microsoft.
Oh, and for you programmers out there, there's a very cool IDE called Omnis Studio, with a pretty powerful scripting language, that is very nice. It too requires a runtime (similar to the framework). Problem is, every computer that runs your program must have a runtime license from the publisher...at about $250 a pop!