It is typical that you can see other computers on the subnet you are on. This is not something I would expect the ISP to block. Most NAT routers will make you relatively safe. Some ISPs equipment has an integrated router/firewall with NAT capabilities, and these should block the traffic you are seeing. This is mostly on newer equipment.
The systems you are seeing are likely your neighbors systems which are not appropriately firewalled. You are likely equally exposed.
As IPv6 roles out NAT will not be used so you should become familiar with appropriate firewalling. The good news is that the ISP should give you your own /64 or /56 subnet. Things like file browsing should be restricted to this subnet and computers within this subnet should be safe. Link local addresses (your side of the router) should not be routed to the neighbors or anyone else.
Unless you need it, it is best to enable sharing services and host discovery on your computer. If you do enable it, only enable the sharing services you need. Enable the firewall and configure it to limit access to local systems.
You say plug into a wall. Are you at a university or business? If so, that is probably your peers/other computer around you. – Theo – 2011-04-09T15:45:04.240
i talk about home network. In the wall i have cable of my isp. – None – 2011-04-09T15:48:08.247
Depending on the ISP it could still be peers inside the same subnet, or if you have an unsecured wireless router you may have uninvited guests. – Theo – 2011-04-09T15:56:55.370
Turn on your router's firewall. Looks like your ISP has your neighbors on the same subnet. – emgee – 2011-04-09T16:10:15.950