These spots are most likely dust or oil on the sensor assembly (technically the filter in front of the sensor), not on the lens. Lens dirt usually does not create small, well-defined dark marks in the same place across multiple photos.

A good clue is whether the spots stay in the same position from shot to shot. Sensor dust/oil will do that, and it becomes more visible at smaller apertures (higher f-numbers), where the spots look darker and sharper.

On some Nikon bodies, excess oil from the shutter mechanism has also been known to reach the sensor area, where it can trap dust. If that’s the case, one cleaning may not be enough and several cleanings may be needed before it stops recurring.

What to do:

• Check whether the spots remain in the same place in every image.
• Test at a small aperture to make them easier to see.
• Use the camera’s sensor cleaning function if available.
• If the spots persist, have the sensor professionally cleaned, especially if oil is involved.

It is unlikely to be bad pixels, since those usually appear as tiny sharp points rather than soft, out-of-focus spots.