If Company B uses ABC’s trademark for business activities, it is an infringement, because Company A’s ABC has been registered with the Trademark Office and is protected by law.

If the products of Company B and Company A are not in the same category (check the product classification table for details), then Company B can use the trademark ABC, provided that ABC is a non-well-known trademark. If ABC is a well-known trademark, then Company B cannot continue to use the trademark ABC, otherwise it will be an infringement.