Microphones can be rather small. If you don't see one connected to the computer, it might simply be in one of the drawers I haven't checked.

[Of which there are twelve: the two lockless middle ones for each desk, and the two lockable top ones for each desk. While there isn't a microphone connected to the computer right now, it's one of several small devices to be found in the middle right drawer of the desk Kay is sitting at right now.]