Frogs are made up of atoms like everything else which surround us. Each of these atoms has electrons around the nucleus. Within a strong magnetic field, these electrons deviate slightly from their orbits. This slight shift, in simple terms, causes many mini magnets of the frog. (Of course, it can do it with the help of the magnetic field that each atom possesses.) Not only is this unique feature of a frog, but many substances such as water, gold etc. have this feature called "diamagnetism". However, not all the materials have a stronger diamagnetic property that the magnetic field can take them off. Frogs can be levitated when they are exposed to a high magnetic field due to their high water content in their body structure and their tendency to be affected by this effect. In the video below you can see this clearly.
