Presumably you're running some kind of terminal emulator on the PC? In which case you need to find out what control code(s) (probably an escape sequence) are required to cause the terminal emulator to clear its screen.

You can't expect there to be a built in function to do this in Keil as it doesn't know anything about PC's or terminal emulators. You need to write your own clrscr() function.

Take a look here:

http://www.holomorphy.com/~wli/doc/vt100esc.html