I have seen this for years now, but never made much of a mention of it. Nobody else seemed to notice, as I'd not heard of any complaints. However, through several tests over the years (and just now), I have confirmed that WiFi often interferes with wireless keyboards and mice. They are all operating within the 2.4ghz spectrum, all-be-it on different channels (sub-frequencies).
Since I almost exclusively buy Logitech, I've noticed this with their products -- even with brand new batteries (or a full charge) and a very close receiver. The WiFi router can be 802.11g or 802.11n, with the latter causing probably more potential for interference due to its MIMO (use of multiple channels).
This ONLY occurs during high traffic periods. In normal traffic you'll probably not see it. For example, a large file copy will cause a disturbance. Try it yourself (note some models may differ).
Now, what to do?
- Obviously the stronger your battery in your wireless keyboard and/or mouse the better the connection. Trust me when I say the strongest battery won't overcome severe RF interference from a WiFi network under heavy load.
- Moving the keyboard/mouse receiver to a line-of-sight location (or as close to that as possible) can help a lot.
- Changing the channel on your wireless mouse or keyboard may help the most -- assuming it really is interference and not just a dead battery. On some models this is available, others it is not. On those other models, try turning the device off, then back on. This is likely to cycle the channel (though I can't say that for sure, and it depends on the model).
- Similarly, you can change the WiFi channel (BTW: there is a great Android app to let you know where the least interference form other networks is),
- Adding some sort of 'shield' between your wireless router and your primary PC (or wherever the mouse and/or keyboard receive is) may help, if your primary PC is connected to the router via a wired ethernet cable and doesn't need to talk to the router. This helps deflect SOME of the WiFi signal. How much depends on the material.
- Moving any network adaptor or wireless router farther away may help
- Reduce router radio power (on modded routers, or routers that have this option)