Can I revert commits directly on GitHub?

No, that feature isn't directly available on the GitHub web interface (as opposed to the "Revert" button recently added for GitHub for Mac/Windows)

Actually, it is for pull requests only, since June 24th, 2014:

Introducing the Revert Button

you can easily revert a pull request on GitHub by clicking Revert:

You'll be prompted to create a new pull request with the reverted changes:

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git revert is a bit more complex to manage through the web as it can accept a range of commits.
It shouldn't be an issue in terms of collaboration though: a revert adds a new commit, it doesn't change the history of existing commits.

If you want to use just github web. There is a tedious way though.

Step 1. Goto commit history, find the commit hash which you want to revert to; and click "Browse repo at this point in history"

Step 2. Create a new branch from this commit hash (say "temp")

Step 3. Delete the branch which had the problem (say "main")

Step 4. Goto "temp" branch and create "main" branch from it. And you're done.

Ofcourse, this is not a good way and it might only work for recently created commits.

You can't revert back to that commit on the GitHub web site, there is no option to do this action, Instead, you should use command-line or GitHub Desktop as below

After REVERT, do not forget to PUSH the code. For more details, check the link How to restore deleted files on GitHub website?

This worked for me (GITHUB).

 1) git reset --hard HEAD^   
 2) git push origin -f

Note:- These lines reverts commit back one by one.