Hi Suneetha,
It happen because the data displayed last time is still there in the ‘display data registers’ of the 128*64 GLCD module. Usually GLCD module have a reset pin. You can design the circuit so that the GLCD get reset while you press the OFF button. You can also control the reset pin with your code, but I’m not sure it will work out. Better you manually reset the GLCD using a seperate switch.
Please post the part number of the GLCD and your complete circuit, so that somebody can help you more regarding this problem.