Abstract: A protective cover or envelope for a keyboard array that prevents entry of contaminants such as water, foodstuffs, chemical compounds, including medical or pharmaceutical compositions in the form of fluids or solids, dust and the like into the interior of the keyboard assembly from the keypad top deck. A membrane of a resilient, substantially transparent, material, such as an elastomeric polyolefin, is used to form a one-piece cover that extends over the keyboard array and preferably at least a portion of the obverse face of the keyboard assembly and acts to drape or enshroud the keyboard assembly on its upper face or deck. Preferably the elastomeric cover is an envelope-like membrane structure of generally uniform thickness and is constructed in a shape that when stretched to receive the keyboard, it covers the top portion of the key array as well as extending at least partially down the side walls of the keyboard and is in proximate contact with the top deck of the keyboard assembly.