Well, after a cardio work out, I'm usually a little lower from sweat loss (if it was a good hard workout)
But no matter what, you have to remember that weight loss does not progress in a linear fashion -- you can do the same things and lose some weeks, stay the same or gain! The scale doesn't just measure the fat you want to lose, but ALL of you. So if you were retaining water for whatever reason, the scale may show a slightly lower loss.
Keep your long term goals in mind and don't worry so much about the scale week to week, especially if you're sticking to your plan! Good luck!
My 5 C's of healthy living: Commitment to conscious control, with the understanding that choices have consequences