Shower in basement is backed up. Wondering if it's because a floor drain is covered up.

Sounds more like the drain line is clogged between the shower and the main stack, and shares venting and drain with your kitchen sink. Have a plumber run a drain snake down from your kitchen drain (after the 'P' trap ) to clear the line. A covered over floor drain should have no effect on the back-up.

Jabberwoky's answer is spot on if it was the main drain any water used would back up. However you need to find the main drain. It should be within a few feet of the front of the house. if your neighbors have similar houses look where theirs are located. otherwise take a heavy stick and bang the floor in the area you think it is in, when you hit a hollow sounding area that is probably it. you can also check the building dept for house plans. the plumbing diagram should locate it if its available

It sounds like your drain lines have clogged, you need a call to plumber or septic solution service if it require pumping.
But it could be a small clog between shower and the main line, a plumber can fix it.

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