Wi-Fi RF signals operate in the (at most) 100s of mW (milliwatts) power range, at the source. But the signal very quickly attenuates, so by the time it reaches your cell phone, for example, it's far less than that.
Meanwhile, your microwave operates in the 1000+ W (Watts) range. But no one worries about microwaves (I'm not saying you should, just giving an example).
There are countless resources online explaining why low-energy radio waves such as from Wi-Fi are perfectly safe. But actually, one of the better sources I've found that does a good job explaining the science behind RF safety and effects on health is from the Canadian government: