An image sensor is provided. The image sensor may include an active pixel electrically connected to a column line and configured to provide an output voltage to a pixel node and a bias circuit electrically connected between the pixel node and an earth terminal, and in which a first current flows through a first line electrically connected to the pixel node, wherein the bias circuit includes a first variable capacitor electrically connected to a power supply voltage, and a second variable capacitor electrically connected to the earth terminal, and the magnitude of the first current may be configured to vary based on a ratio of a capacitance of the first variable capacitor to a capacitance of the second variable capacitor. The output voltage may be configured to be adjusted based on the magnitude of the first current.