Braking system

When braking the car stops ok , but after a few secounds the car will start moving again. Pressing the brake again will stop the car. A mechanic replaced the Master cylinder, but the pedal seems to travel to far before the brakes are applied. Pumping the brakes a few times bring the pedal up farther, but that procedure has to be done every time. Could the problem be with a electronic part of the braking system?

Am I understanding you right? You drive in traffic, stop at a red light, brake. you release the brake and the car begins to move. All cars do that, it's because the engine at idle is turning fast enough to make the car want to move, so thats what it's doing.

Or do you mean when you cut it off and your parked on a hill or something?

When braking the car stops ok , but after a few secounds the car will start moving again. Pressing the brake again will stop the car. A mechanic replaced the Master cylinder, but the pedal seems to travel to far before the brakes are applied. Pumping the brakes a few times bring the pedal up farther, but that procedure has to be done every time. Could the problem be with a electronic part of the braking system?
After the intial stop, without releasing the brake the car will start moving. The brake pedal slow goes to the floor. depressing the brake again will stop the car. This process stops once the pedal is at the floor.

Good possibility you have air in the brake system!! You will need a good brake bleed procedure.