Only if you use plain IRC. If you use something like irccloud, that is prevented. Which can be thought of as a "webwrapper" for IRC. I have been using it for some time now and I enjoy it.
I use WeeChat (https://weechat.org/, running on my server) and Glowing Bear (https://github.com/glowing-bear/glowing-bear) to connect to it from wherever I am (desktop or mobile), it works very nicely. Because it's self-hosted, it has higher setup overhead than signing up to slack, of course. But it does solve IRC's mobile and multi-device problems for me wonderfully. (I'm one of the Glowing Bear developers)