His answer: Most definitely, Yes!
According to Obama:

It’s important to distinguish between posts that are public — social media on a Facebook page — versus private communications through various social media or apps. And our law enforcement and intelligence professionals are constantly monitoring public posts and that is part of the visa review process — that people are investigating what individuals have said publicly, and questioned about any statements they maybe made.

This might even affect your private posts if they consider you a threat – in his own words

But if you have private communications between two people that’s harder to discern, by definition. And one of the things we’ll be doing is engaging with the high-tech community to find out how we can, in an appropriate way, do a better job if we have a lead, to be able to track suspected terrorists.

In summary, for now, it is just your public posts that will be monitored, but there is a big possibility they might monitor your private post if they consider you a threat.
At the end of the day, We’re all being held accountable for the things we do that are tied to our name, publicly. So mind what you tweet or post. You are being monitored!