In this paper, a new method was proposed for the navigation of a mobile robot in an unknown dynamic environment. The robot could detect only a limited radius of its surrounding with its sensors and it went on the shortest null space (SNS) toward the goal. In the case of no obstacle, SNS was a direct path from the robot to goal; however, in the presence of obstacles, SNS was a space around the robot where fewer or no obstacles existed. In every time step, the robot went to null space. The simulation of robot navigation by SNS method showed that SNS can be a simple and very robust method.