A computer accessory tray assembly adapted for mounting to a chair. The tray assembly includes individual left and right mouse trays mounted by horizontal arms to respective arms of the chair. A keyboard tray is engageable with the left and right mouse trays to prevent lateral movement of the keyboard tray, but allows the keyboard tray to be lifted up from engagement with both mouse trays and moved out of the entry/exit position of the chair so that the user can have access to the chair. When removed from engagement from both mouse trays, the keyboard tray can be stowed by hanging it from either of the mouse trays. The mouse trays are adjustable vertically, forwards and backwards, and can be titled to provide ergonomic access to a mouse resting on either mouse tray.