In Brazil we don't have a specific word for mouse pad.
Mouse pad will still be mouse pad. Like a lot of words or expressions relative to computing, basically.
For example:
wireless, mouse, backend, frontend.
A example in a sentence:
Ganhei um mousepad quando comprei um novo computador.
in english will be like this:
I got a mousepad when bought a new computer.
All of these examples above are perfectly understood in Brazil. No need to translate them.
These words, usually english words, are called "estrangeirismo", when habits start to accept a foreign word as a native of your language.