This occurs due to electrostatic charge means the charges which are at rest. When the comb is rubbed with hair it gets charged, and when the comb is brought near the neutral paper strips than within the papers strips, the electrons get either repelled or attracted according to whether the comb has a negative or a positive charge. This makes the paper strips have an unlike charge in the direction of the comb, and makes them to get attracted towards the comb as shown in the figure below.