A modular computer user interface system particularly adaptable for use with portable computers and comprising the integration therewith of at least one, but in certain specific embodiments, a plurality of auxiliary modules, such as keypads, interfaced with the processor independent of the conventional keyboard. The one or more auxiliary modules may be permanently secured to the platform of the portable computer in spaced, segregated relation to the keyboard and keys associated therewith. Alternatively, one or more of the auxiliary modules may be removably mounted on or detachably connected to the platform and keyboard, wherein regardless of their fixed, removable or detached relation to the platform of the computer, each of the auxiliary modules are independently operable to effect data and signal communication with the central processor of the computer, independent of operation of the conventional keyboard. The plurality of auxiliary modules may each be independently structured to perform various functions and therefore are independently operative as a numerical keypad, a proprietary keypad for processing specialized software and/or another type of user interface module.