I have got a US Business visa (B1/B2) from my past company, but I didn't travel. Now I have an opportunity to go to the US for my present company. Shall I use the same visa?
Note: The visa is multiple entry and no company name is on the visa.
Yes, you can, presuming that the travel still falls within the category of what a B1/B2 visa allows.
If your visa was restricted to travel for a specific employer then the employer name would be listed in the "annotations" section on the visa.
However if there is nothing listed under the Annotations then the visa can be used for travel for any company.