Laptop starts back up on its own

[Trey Sizemore]

First time I've seen this happen...I've installed FreeBSD:

FreeBSD laptop.fbsdsizemore.com 5.1-RELEASE FreeBSD 5.1-RELEASE #0: Thu 
Jun  5 02:55:42 GMT 2003     root at wv1u.btc.adaptec.com                
:/usr/obj/usr/src/sys/GENERIC  i386

on my laptop.  When I shut the PC down at night, I wake to find it back 
on again a little later.  Today I shut it down, left the house, came 
back and it was on again.

I shut down by entering 'shutdown -h (or -p) now' at the command line 
and then depressing the power button after it says OK to power down or 
'press any key to restart'.  It does power down completely and then a 
little later (not sure how long it takes), it's back on again.

Looking for some things to check to get to the root (no pun intended) of 
this.

Thanks-