Dose of what? Radioactivity, due to the measurable quantity of potassium-40 in any banana. This radioactive element could be forgotten if the calculator has only two digits, 0.0, but adding one more it's approximately nothing.
The body doesn't accumulate this element specially and it cannot could be analyzed as a risk for health. There are revealing experiments with these fruit and Geiger counters on the Internet that provide a definitive insight on the matter, far from being a worry.
It's well known that the Earth has a radioactive background that was there during millions of years. As always the problem appears with strong emissions of energetic particles to delicate organic tissue that experiences damage with them, or radiation sickness with high doses in a short period of time.