Removed lipoma attached of my skin in the forehead, is this normal? (photo)

When lipomas are removed there is a void--an empty space that should be filled.  A plastic surgeon utilizes techniques like "undermining" and "multilayered suturing" in order to pull the deeper layers over the bare bone and fill in the deficit.  Usually these techniques fill the hole in very well and allow for normal movement and appearance of the overlying skin.  When the deeper tissues (fat, muscle, fascia) are pulled together they act as a "spacer" that prevents the skin from sticking down to the bone.  Unfortunately, not everyone heals the same, and sometimes the sutures don't hold or the deeper tissues tear and retract, leaving a depression, and without the spacer the skin may stick down to the bone.  
Thankfully this can be corrected, but usually requires a second procedure.  There are 2 common ways we approach this: 1) fat injection or 2) dermal fat graft.  Fat injections involve sucking some fat from another area of the body (often through a small incision in the belly button) and then injecting the fat with a needle between the skin and bone on the forehead.  Sometimes this procedure needs to be repeated a second time to get enough fat in place.  A dermal fat graft is a little different.  It involves excising a small piece of skin and fat from somewhere else on the body, removing the upper layers of the skin (the epidermis), leaving you with a "dermal fat graft".  The scar from the lipoma is re-opened, the dermal fat graft is sutured over the bone, and then the skin is closed back over the graft.
I hope this helps!