Could be that the rotors are "out of round" and pulsate
Could be a malfunction in the ABS system
brake switch located on the top of the brake pedal
Check the switch adjustment on the brake pedal arm.
out of brake fluid?
Warped brake rotors.
More than likely it is the brake light switch that is attached to the brake pedal.
Pushing on the brake pedal
One of the main causes of feeling a vibration in the gas pedal is engine vibration. The vibration from the engine causes the accelerator cable or linkage to vibrate and the vibration can be felt in the gas pedal. Check with a mechanic to be sure.
Typically, that comes from having air in the lines.
Check the bulbs, fuse & brake light switch on the pedal.
check your fuse and your brake light switch on your brake pedal lever.
BAD BRAKE LIGHT SWITCH AT TOP OF BRAKE PEDAL
Check the brake switch located on your brake pedal shaft. May have to be replaced.