You don't have to store almond butter in the fridge, but it's not a bad idea. The reason it's better to keep almond butter in the fridge than in your pantry or kitchen cabinet is simple. Even though a jar of the stuff is shelf-stable for up to two years when unopened, almond butter can go rancid. As Janet Rausa Fuller explains in Epicurious, open jars of nut butters only last two to three months when stored on the pantry shelf. The easiest way to prevent your almond butter from going bad and extend its shelf-life—by as much as twice as long—is to pop it in the fridge.
Keeping your almond butter in the fridge is especially important if you tend to purchase nut butters without preservatives or if you like to make your own nut butter. MaraNatha is a company that makes organic nut butters, and they note that because their nut butters have no preservatives, "they can become rancid if left out of refrigeration for an extended period of time and/or exposed to warm temperatures." They do, however, also add that refrigeration isn't required if you, "can keep your nut butter in a cool, dark place" and "use the contents of the jar within a reasonable amount of time."
There's one other benefit of keeping your almond butter in the fridge, besides extending its freshness and shelf-life: preventing oil separation. When you keep almond butter in the fridge, it's easier to work with because you don't have to stir in that layer of oil that tends to separate from the nut butter itself when stored at room temperature.
The flip side is that almond butter will solidify in the fridge, making it more difficult, if not impossible, to spread on your piece of toast or slice of apple. But keeping your almond butter in the fridge is the best way to make it last as long as possible and protect your investment, because that stuff's expensive!