Yes. If you do not want a particular user to be able to access their Genovo account for any reason (e.g. they’ve left the company), you can do this with the click of a button from with account admin > manage users by simply setting their account to not approved and clicking save.
However, please note a deactivated / unapproved user will still count as an active user for the purposes of your account's User Limit. When you max out your User Limit, the only way to free up a user account so another user can be added afresh is to delete the user who is no longer required. Please read this article and this user tip blog before deleting a user.