How old is the house? If 15+ years, it is possible that you are seeing a sink hole or a sink hole that's been repaired and is still sinking. This happens when builders buried construction debris (including tree trunks) into pits. Over time, some of the material decomposes and the area settles. Sometimes a hole will open up even (my leg fell into one). You can test for this by taking a study metal rod(a piece of rebar is good) and driving it into the center and other spots. If it goes in easily, chances are you have some empty space in there. Just topping it with dirt will not fix it in that case.

Previously "fixed" sink holes may continue to settle some. My neighbor put several DUMP TRUCKs of fill in her sink hole and she still has a depression.

Anyhow, no need to pull up any grass prior to adding dirt and reseeding. Best to reseed fescue in the fall if that is what you have, not now.

Thanks! It was built in 86 so I dont think it is a sink hole - However a deck was added to the back of the house and it looks like a tree was moved to make room. The depression is right in front of the deck.

I will take a picture and post it when I go back to the house.

Oops - I am sorry I thought you meant at first 15 minus years. Ok, I will try to find a piece of rebar from somewhere and use that - I am guessing I have fescue.....