What wireless? what are the PCs specs?
That's not normal, but I'm suddenly having issues where my Intel 5100 WLAN intermittently drops down to 100K, it had been working fine.
A generic RALink wireless n works fine, and the 5100is behaving now that it realizes I'm onto it.

It's not "normal' for Linux to have wireless issues, if anything, less issues than Windows.
...but some chipsets are not as well supported as others, due to lack of help from certain manufacturers not releasing full specs, and things having to be reverse engineered.