Average velocity increases as well.
Work Step by Step
In gases, the molecules move around randomly in many directions, causing them to have a much higher average speed than average velocity. However, there can still be a net direction of the molecules. Therefore, since the molecules are moving faster on average, they will have a higher average velocity if the particles' net position is changing. If the particles are in a container so that the net position of the particles is not changing, the average velocity will be zero regardless.