'WebProcess' IS Safari
Safari launches a separate WebProcess task to deal with loading and rendering any web site you visit. If you want to get rid of WebProcess then quit Safari, but somehow I don't think that will solve your problem.
I think you really mean your problem is the pop-up window, and THAT is what you're trying to stop.
The likliest cause for this is the Parental Controls feature of Mac OS X that limits access to kid-safe sites. If you're the administrator of your machine then you can either turn off Parental Controls or change the access rules.
If you're not the admin of your machine then go talk to your parents