The keyboard function is classified as a "Debugging and Analysis" function, that's the category in which its documentation page is classified. That falls into the first of the categories given on this documentation page which lists a subset of functions that are not supported for compilation in MATLAB Compiler. The keyboard function is explicitly listed on that page as not being supported.
If you describe how your application tries to use keyboard we may be able to suggest if there's an alternative (pause, perhaps?) or if what you're trying to do is fundamentally incompatible with MATLAB Compiler.
