Well, yeah..
Sure.
When married men do this it's called coveting (which is a sin) and further, it hurts your wife.
It says to her that she's not good enough and you want to look at pics of anna. That's definately both sinful and mean.
But, physical attraction does bring people togeather and into the marriage covenant in the first place so, like most things it's not the attraction but what you do (or don't do) with it in the confines of marriage that's bad. Not the attraction itself.