No, it is not. There are legal implications to using another company's domain name. Some marketing professionals recommend that new businesses use a domain name of another company with the suffix as only a differentiating mark. (An example is a .biz instead of the .com used by the other company.) This strategy is meant to siphon the other company's potential customers to a new business that is at its establishment phase online.
At times, a domain name previously used by a company (that happens to be your competitor) is up for grabs. Some marketers also recommend purchasing this to redirect business to yours.
In either case, both practices are not good for a new business. People may perceive your website as spam or a phishing website, which is not good for your credibility. It is best to register your domain name with your company's name or trademark.