Depending on what application you are using, and what files are open, it can be perfectly normal.
It can be normal to use over 95% of the physical memory plus a fair amount of virtual memory, but, in some cases, it may indicate that an application is leaking memory. Eventually, the problem application will crash by itself and cause the memory to be reclaimed.
It's no longer as much as a problem as under Windows 9x, as memory management have greatly improved and any leaked memory is recuperated when closing the leaking application, or when it crashes.
An apparently simple web page may be loaded with tons of unseen stuff, like java applets and flash objects. It may have multiple, overlapping, images. It may contain lots of links that appear as a single word but that are effectively near 1000 characters long. It all adds up.
Play a video, and you may find yourself using more than 1 Gb only for the video file.
Anything under 90% memory use can be deemed normal, and even more can be normal.