One beer isn't going to do you much harm, even if it's a habit, it could be worse.
If you want to know if it's a problem, just see how easy it is to not have one tonight.
And if you say "well, I'll try tomorrow, not tonight because <excuse>", then ask yourself again.
If you could switch it for a glass of red wine, you would actually go from big calorie intake to good for the heart.