There are two exceptions provided in the ITA where the corporation is not considered a PSB:
If the corporation has more than five full-time employees (more to be emphasized) throughout the year. In such a case, the corporation is carrying out an active business even if the other tests for a PSB are met.
If the income coming to the corporation as a result of the services provided by an incorporated employee is an associated corporation.
With regards to more than five full-time employees, if a corporation has five full-time employees only, the exception is not available. However, an extra part-time employee can help with getting this exemption.