Cement powder is a mixture of sand, lime and mortar. When the cement powder gets wet it turns into liquid cement and when it dries it will harden. On its own, cement powder will not stain wood. If the wood was wet or if you dropped water on the cement powder, this would leave a hard cement stain on the wood. To avoid damaging the wood use sandpaper and solvents to remove cement.
Rub coarse sandpaper over the surface of the cement stain. Don't sand the wood as this will scratch it. Rub the cement until just before you reach the surface of the wood.
Dust off the area to remove as much of the cement dust as possible.
Rinse a cloth in clear water and rub it over the area to remove the rest of the dust.
Soak a clean cloth in white vinegar.
Lay the white vinegar cloth over the cement. Let it sit there for several hours. Re-wet the cloth as needed to keep it wet.
Remove the cloth and scrub off the remaining cement with a scrub brush. Because there is not a lot of cement, the mild acid white vinegar will be able to soften it enough that you can remove it.
Wipe the area with the water-dampened cloth.