Of the known ways for electromagnetic radiation to harm cells (directly breaking chemical bonds when a molecule is hit by a photon, and heat damage from the energy absorbed), we are pretty sure that wireless headsets and cell phones are safe.
The frequencies they use don't involve photons that can break bonds, and they don't have enough energy for heat damage.
The open question is whether or not there are either unknown ways it can harm cells. An unknown direct harm method is probably unlikely. There have been enough studies that we would have spotted it.
An unknown indirect harm, though, is harder to rule out. An indirect harm would be something like it can't cause cancer, but if a cell goes cancerous for some other reason the electromagnetic radiation interferes with the body's mechanisms for detecting and fixing or killing the cancer cell.
Keep in mind that even if these things do increase risk, either by some unknown direct mechanism, or by an unknown indirect mechanism, we can say that the risk increase is low. You probably do dozens of other things a day with similar or more risk that you could avoid.
Bottom line: if you want to have a wireless device next to your head all day for convenience or out of work necessity, no one can really say you are being foolish or cavalier toward you health. But if you decide to minimize such device usage, no one can really say you are worried over nothing.