You can check the airspeed reading with Mission Planner or INAV configurator. Just blow on the pitot tube or press your finger over it and observe the response. In still air oscillation between zero and small values (2-3/s) is normal.
The airspeed varies with the square root of the pressure, so for differential pressures near zero it varies quite a bit with very small pressure changes, while at flying speeds it takes much greater pressure changes to produce a similar change in speed.
If you see mostly 0~2m/s, with an occasional bounce to 3~4m/s, consider it normal. You will not see that sort of variability at flying speeds.
