Hi
you need to find whether its the front or rear first, if its the rear, its more than likely something your mechanic has done, especially if you hav'nt had any issues prior
can't see it been the master cylinder, I've never seen one fail that makes the brakes stick on, they either leak or the seals fail and the pedal goes very low
If its the rear brakes that are binding, jack it up and find which side it is
I'd check if the adjusters have been set right, if they been set too tight they might seize as they get hot, if there's no enough clearance
also if the adjusters are set correct and the hand brake cables are free, Ive seen copper brake pipes crimped incorrect so that they trap the fluid
cheers
Joe