Definitely efflorescence. I've had this happen from water seeping up from below the concrete in a basement, and I currently have this in a garage where the water comes in on the car and when it gets to the concrete leaches out some of the minerals (not sure, some form of calcium or calcite?) and crystalizes as the water evaporates.

The only case that needs remediation is when the moisture is coming through the concrete (so, not the garage example above) and has enough actual water moving to pool on the surface. Other than that just sweep or vacuum away. Don't breathe the dust if it gets airborne.