An apparatus to measure noise in an image signal and a method thereof. The apparatus includes an area division unit to divide an image signal having noise therein into a plurality of areas and to output area information corresponding to the plurality of areas, a variance calculation unit to calculate variances of the plurality of areas using the area information, the image signal and a noise-attenuated image signal obtained by attenuating the noise from the image signal, and a noise determination unit to determine an amount of noise in the image signal by comparing the calculated variances of the plurality of areas. Accordingly, the noise measurement apparatus can measure the amount of noise irrespective of characteristics of the image signal, and thus noise attenuation can be performed more accurately.