Is it bad if my atrial fibrillation is around 150 beats per minute?

Potentially : Yes. You are likely to have symptoms of palpitations, shortness of breath and chest discomfort . Also if your heart rate remains elevated for long periods of time it can cause a decrease in heart function. See yoyr doctor asap.

Not great: The latest data available to us from the clinical trials suggest that an appropriate target is a resting heart rate less than 110 bpm. Periodic rise in the heart rate to greater than 150 BPM is not harmful, however if this is your rate the majority of time, cardiac dysfunction may eventually result.