Oh, ok. Since the file is stored on your computer, you will need to do this:
Using a computer language ( I recommend C#), create a program for your PC that reads the file and then sends it to your nxt via a serial port with a bluetooth dongle. You will have to know how to read the .mat format, which you can figure out by looking it up or by contacting the developer of your matrix editor. Have an nxt program that reads the incoming messages and uses them.
Of course, there are downsides to this: You will likely have to learn a new language, purchase a dongle (although I think somehow you could use the USB cable as well), and spend much time. Thus, you may want to consider manually hard coding in the matrix straight to your robot. That, too, can be time consuming.
A third and final option which would probably be best (I saved the best for last
) would be to find a program on the web already written to do what I described in the first option with a USB cable. The only problem with that is seeing if such a program exists.