Is this normal in a relationship? Or is my girlfriends mom seducing?

Awesome. Maybe you can get a mother-daughter threesome Lol. I'd wait till her mom actually makes a move on u tho. Like verbally bringing up sex out of nowhere or making excuses to touch you. Otherwise you are gonna find yourself in a hell of an awkward situation if you are misinterperting things. Haha shit would make a good movie. 'Stacy's mom: the movie'