Go into your wireless router's setup screens (for how see literature which came with router). In router go to Attached Devices which will list all connected computers (your own will be there by name and/or MAC ID).
You could also look at Wireless Access List.
If you have WPA or better wireless security, chances of anyone getting in are slim.
Of course your wireless adapter's scan facility will reveal other wifi routers, but no wireless adapters except those already in an ad-hoc link between adapters/computers.