Well, if you want to be pedantic about it, so is solar, wind and tide energy. The sun will transition to red giant in a few billion years then (probably) become a white dwarf. No more sunlight. And even longer after that, as the universe is expanding, due to the law of entropy, everything will eventually be spread out thinly across space, and the energy levels will be constant everywhere. So if you want to be pedantic, EVERY source of alternative energy will run out eventually, but the person asking this question obviously wants to know what alternative energy sources are exhaustible in the timeframe of human existence, and the answer to that is biomass and nuclear (with the current technologies, the figures show we will run out of uranium in about 160-200+ years, but potential new technologies look to be able to extend our uranium supply almost indefinitely). And technically we can run out of (useable) biomass.
Realistically, we're never going to run out of biomass, though producing enough to satisfy fuel demands could be very difficult. Efficient use of current technology and (more important) fuel recycling means that we're unlikely to run out of nuclear fission fuel, either. We're never going to run out of nuclear fusion fuel.
Geothermal is tricky. We're never going to run out of geothermal energy to tap into (as that would require cooling of the earth's core, which won't happen on a human timescale), but individual places where geothermal energy is available can easily change, and as geothermal isn't portable, it is entirely possible for a given location to be unable to produce geothermal power at some point.
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