Yes. Not only is it adjustable, we highly recommend you adjust it!
Everyone's head is different, so try pulling the earpieces in and out of the forehead band to adjust the headband's size (similar to adjusting a pair of headphones).
The Muse headband is designed to fit most typical adult heads. Not only was it ergonomically designed for comfort and fit, but we were also concerned with finding a shape that could fit snugly and apply the right amount of pressure to get good signal quality. This is why adjusting your headband size is important.
Even if it's comfortable, your size may not be providing ideal conditions for good signal quality. Adjust your headband a few times until you find a size where it's easy for you to get good signal quality in the app relatively quickly.
For more information on how to get the perfect fit, feel free to check out the videos below: