Top shows many Odoo process. So I guess you have enabled workers.

Depending on your server setup and your Odoo config file, this can be quite normal, even without any user. Because Odoo allways run, so it answer fast when someone try an access. The load depends on various factor : ram, cpu, network, hard-drive speed and other services running on the server. Without further informations it is hard to tell you if something is wrong.

On my well configured little server, the load is allways high (around 100%)but doesn't increase when someone log in. Odoo and Postgresql are setup to allways use the whole Ram and CPU available.