If these domains are the same where two are, aliased to, or parked under the one main domain, then yes.
Aliased or Parked domains are domains that you own, but which do not contain any content. Instead, they point to the contents of another domain or subdomain on your account.
This means the index page is the same page for all 3 of these domains.
Use canonical URLs to inform the search engines they are the same site.
There are various ways to pass the canonical URL to the search engines If not you will be penalized fro having duplicate content on multiple domains. This also applies to sub domains. Google sees http://example.com and http://www.example.com as two different domains.
IMHO I think embedding the conical link in the HTTP Response Header is the best and easiest method.
I do not like using a redirect but may be necessary in some cases. For example all the internal links are http://example.com then adding a 301 permanent redirect to http://www.example.com
All the details are at this link: Use canonical URLs