There are some Arduino boards that can do it using this library. https://www.arduino.cc/en/Reference/MouseKeyboard
I haven't used it.
Jim

On 2015-12-05 11:10 AM, William Park wrote:

Hi guys,

Do you know a way to emulate a USB keyboard using Raspberry Pi,
BeagleBone Black, ODROID, or some other embedded board?  That is, as far
as PC is concerned, it's receiving keypresses from some keyboard.

I know those boards have UART pins.  But, even if I connect the pins to
a serial-to-USB cable, the USB end of the cable will show up as serial
(/dev/ttyUSBx) and not as keyboard.  I have such a cable, and that's
what I see.