Is it weird to display ads on an academic website?

Such a website is itself an ad: for the lab, the lab's research, and for the personnel running/working at the lab.

In many ways, a lab website is like a resume. While it's not unusual for newsletters published by some local org (say, a school, church, youth group, etc) to have local ads to cover publishing costs from the neighborhood dental clinic, grocer, etc, but you wouldn't expect to find these on a resume.

Probably most people are conditioned enough to online ads that they wouldn't even notice them, but if they did it might seem a bit weird, and if they were at all intrusive it would be downright ugly looking and reflect badly on the lab. If I were working in a lab where the PI had a website with ads, I'd be embarrassed by it even though it wasn't my own responsibility. If I was visiting such a site, I might wonder if I've stumbled on some illegitimate content farm site by mistake.

I doubt a typical academic's website gets anywhere near enough traffic to make ads make much sense financially. The cost of potentially putting off a precious visitor doesn't seem worth it to me to pocket a few pennies.

If the site is hosted by the university or with any grant funds for research it is likely illegal or against some terms to make any personal profit off such a site; even if the funds are just used to pay back the site costs it's a gray area that is still probably not allowed. A university could certainly even have a policy on this even if their funds are not directly involved if anything about the website affiliates it with the university, including being an official or pseudo-official website for a lab operating out of that institution.

It's just not worth the potential conflicts from any angle I can see.

I'm not quite as negative as the other current answers here. I don't think it is unethical, for example, provided that the domain is your own. Weird, perhaps.

But, a warning. Don't sign up with some ad "service" that has the ability to place ads on your site according to their judgement, not yours. You will regret it pretty quickly, I'd guess.

However, there is unlikely to be any financial advantage to you unless you have a blog with millions of readers. And most of the folks I read (blogs) have periodic campaigns to solicit contributions. But they are also "in the business" of writing daily on subjects of interest to a wide audience.

Of course, academic authors often have "ads" on their web sites to enable potential readers to find their books. I doubt that anyone would object to that.

I don't think I would call it "unethical," but certainly weird and borderline unacceptable.

While I'm sure the idea is to just recoup server costs; it would strike me as very weird to try and profit off visits to your personal website and I would probably avoid visiting it again.

If you were being interviewed, I can't see it being a positive.

Also keep in mind the ads may be targeted. I don't think someone seeing a male enhancement pill on your website would be very impressed, even if it was their own search history that suggested it.