Is a Nikkor Non-AI (Pre-AI) lens mount compatible to a Nikon D90?

Is a Nikkor Non-AI (Pre-AI) lens mount compatible to a Nikon D90?

No - non-AI or pre-AI lenses need to be modified before being mounted on your D90.It could damage the mirror!
See Thom Hogans useful guide;
http://www.bythom.com/lensacronyms.htm

It will physically mount but you'll get neither autofocus (of course) nor metering. Such a lens would likely end up as a paperweight as it's just too inconvenient to use.
Edit:
deepblue is correct, they need to be modified. Otherwise they won't mount at all though, according to this chart:
http://www.kenrockwell.com/...y-lens.htm
Interestingly, they mount on entry level Nikons. I guess it has something to do with the AF motor…