An object in motion has a negative velocity when the movement is in the negative direction relative to the observer. Whether velocity is positive or negative only indicates the direction of the movement of an object.
The velocity of an object indicates the rate of distance traveled over time. Velocity is a vector that measures speed and direction. The speed of an object cannot be less than 0, because an object at rest has no velocity, as velocity indicates movement. A moving object with a speed that is decreasing over time has a negative acceleration, rather than a negative speed.