I found a cement slab that sits about 6 inches below my drive way it is a cement slab that is 5ft x 5ft with 9 1/2 inch circle in the middle of one end of it. It's weird I had never seen anything like it.

Wow, that's a large slab. Is it buried ? How deep ? What caused you to find it ? Have you been doing renovations or something ?

Very interesting to say the least. I'd be wanting to pull it up to see what's under there. You might have stumbled upon something amazing.

Maybe it is a freestanding flag pole base.

Can you dig down where the hole is? Are you sure it is a slab and not something bigger?My first thought was an old septic tank.

I have seen a lot of them. I believe what you found is an old cistern. Dug up many on job sites digging around old houses. If it gets too old it needs filled in. The code here is if its inactive and empty then fill it in