A Q&A on the PlayStation Blog made it clear that a paid PlayStation Plus subscription is not required to play The Elder Scrolls Online on the PlayStation 4.
A PlayStation Plus membership is not required to play The Elder Scrolls Online. PS4 players will only be required to pay the same monthly subscription associated with The Elder Scrolls Online that PC and Mac users will pay—nothing more.
Bethesda did confirm to Joystiq that the additional cost of Xbox Live Gold will be a requirement for the Xbox One version of the game.
The Elder Scrolls Online is slated to be released on April 4 for the PC and Mac, with the console versions coming in June.