No and Yes ,C# is created by Microsoft for their Framework named .Net and C# programs will run only in platforms where .Net is running i.e.. dotnet rumtime.Like windows mobile also use processors and these mobiles have .Net Runtime so C#(.Net) programs will run on a windows mobile.
But in general their is no way to use C# in MCU like of PIC,ATMEL,MOTO.. etc.But at the root we all are using assembly to instruct the MCU for example when we write a C code then compile it ,the compiler converts the logic to assembly.
Use C to programe MCU, its still the best system programming language.