In an interview with the Financial Times, Sony's CEO Kenichiro Yoshida has admitted that the company is working on a new console, which is more than likely going to be the PlayStation 5 (although that name has yet to be confirmed). A number of sources have speculated that the PlayStation 4 successor will see the light of day in 2019 or 2020.
https://www.notebookcheck.net/Sony-finally-confirms-PlayStation-4-successor-is-in-the-works.337786.0.html