It can be normal for motors to run hot. For example, some stepper motor specs that I have seen show a maximum operating temperature of 80 degrees C above the ambient temperature, which means that your motor could be operating within its specifications yet be hot enough to cause a serious burn if you were to grab it and hold on. Some drivers will reduce the current through the motor windings while the motor is idle, which can help to reduce the temperature. Using metal motor mounts can help in heat-sinking, which can also reduce the motor temperature.