Can any one tell me where can I view the list of Opportunity Contact Role object in a separate tab just as we see separate tabs for contacts, Leads, Opportunities ?
opportunityContactRole is a junction object between Opportunity and Contact. It can only be customized through the picklist for Role
You view the OCR through either a related list on the Opportunity page layout and/or the Contact page layout. If not appearing, then customize the page layout to add it.
Contact Roles on the Opportunity can be edited by going to Customize / Opportunities / Contact Roles on Opportunities.
You can't display contact roles on a tab unless you're using a custom object.
Here's a blog post that gives more information on contact roles and examples of the type of picklist values used by other companies.