Is steeped tea sterile?

No, but it may as well be considered sterile for normal purposes. Boiling doesn't actually kill everything - endospores and also fungal spores are ridiculously hardy, and you'd need to autoclave (steam at high pressure) in order to really kill everything. And microbes are everywhere, so the tea is going to get colonized again really quickly unless you pay special attention to making sure that that doesn't happen. Don't attempt to can or store the tea, if that's what you're trying to do. Also, if you're attempting to use unsanitary water to make tea, be aware that some bacteria and fungi make toxins that can't be destroyed by boiling, so even if you manage to kill off the microbes, you can still get sick.

For sterilization, you need to boil something for a minute or more.

Generally, the boiled water is poured into a room temperature container over top of room temperature tea leaves. The tea itself is never supposed to boil.

So, since it hasn’t been boiled to sterilization, no, it’s not sterile.

But if the container is sterile and the tea/teabag has come pre-sterilized, you’ll be pretty close.

If a) you actually got it to a rolling boil for a sufficient time (some teas recommend heating to less than boiling temperature), b) the water boiled in the cup (as in, microwave rather than tea kettle you may have let cool a while before actually pouring it in the cup), and c) you took surgeon-like steps to avoid contamination during and after the steeping process, I'd imagine it'd be just as sterile as any thing properly sterilized by boiling would be.

I would think so? Unless it has in it some of that weird archea that normally live around 200º undersea vents.. I'm sure they'd find your tea to be quite a nippy environment.

EDIT: Disregard. I misunderstood what seeping is.