why am I turned on by woman?

I am not a lesbian but I have enjoyed making out with girls in the past but have tried not to. I love my relationship with my husband and love it sexually too! But I get really turned on if I see a woman rather then a man. Is this a normal thing or something I need to completely try to block out of my head? My husband knows this and it's not something I am hiding from him.  Just wondering if others have felt like this or not?