When we stop pedalling, the bicycle slows down and eventually comes to a stop. This is as a result of

• When we stop pedalling, the bicycle slows down and eventually comes to a stop. This is a result of frictional force between the tyres and the road.
• It comes into effect when there is a relative motion between two surfaces that are in contact with each other and it always acts in the opposite direction to that of motion. 

Therefore, 'Frictional force' is the correct answer.