Is it unethical to publish the results with the known mistake?
Of course, it is, unless you disclose your mistake. If you disclose your mistake in a publication, the only way to publish your findings would naturally be a submission to a low-quality venue. Junk results belong to a junk venue. This might be fine with you.
As for the impact of a hidden mistake, in some fields, folks will read your publication and perhaps care or reuse the data, whereas in other fields, your paper would be write-only. It's hard to say what the impact of a hidden mistake would be.
However, ethics is not the main point here. Regardless of ethics, and even if the impact of your mistake is zero:
If you value your own self, in particular, what you say and write, then tell the truth, or at least don't knowingly lie. Lying is not healthy and doesn't do you any good in the long run. Build and maintain the habit of being truthful as much as you can. For your very own benefit.