I would love to be able to find the study that was conducted on the amount of alflatoxins present in convetntional PB vs. Organic-grind-your-own at the health food store.  Unfortunately, although I read about the study some time back, I can not find a link to post it for you.  However, it was found that the organic peanuts found at your health food stores are  actually higher in the carcinogenic mold than conventional stock.  This might be due to the fact that depending upon the time and conditions in which the nuts are stored, they may stand a greater chance of developing mycotoxins  than nuts in conventional processing plants.  In the case of the latter, the peanuts go from orchard to processing plant in less time than the peanuts which are stored in health food stores and waiting to be ground up by costumers.  Temperature and humidity also play an important part.

None the less, ALL peanuts contain aflatoxins, and no aflatoxin is good.  This mold is also present in corn, but perhaps not as high as in peanuts.

A better bet is almond butter.  Although mycotoxins have also been found in almonds, it occurs with less frequency and at lower concentrations.   Beside the advantage of less fungal toxicity, almonds have a better fatty acid profile in addition to a great source of protein and many other essential nutrients.

Almond butter is quite expensive, which is a deterrent for many.  However, if you are fortunate enough to live in California, or any other state that has a Trader Joe's, you can find a very nice jar of almond butter there for less than anywhere else.