It might be, but nothing is for sure yet, no matter if it was a real act or terrorism or not , the act itself in killin those 14 people it is an act of terror. No matter of which ethnicity the attackers were. Sad things happen in this world these days.
Terrorism is the use of violence and threats to intimidate or coerce. This couple had enough ammunition and bombs to use mass violence that would clearly intimidate those being acted upon. Per a news article, there were a few Christians and a Jew who were slaughtered. The Jew had recently been clear that the shooters beliefs were not that of peace. The Jew was killed. It was also stated the shooter had been in contact with some extremists.
In my opinion, the mass shooting at San Bernadino might not be an act of international terrorism, but it definitely was an act of terrorism with the USA. As far as I am informed from the media, the attackers had planned the shooting, and they had also stored explosives. For me, this premeditation of their actions underlines an act of terrorism.
At the risk of erring on the side of NBC's 2004 election night conservatism, this is simply too close to call and too soon to tell. Let the process work, let the investigation work and draw conclusions based on fact before it is labeled as anything. I'm not an expert, but I'm pretty sure Muslim's are just as allowed to go crazy individually as are any other group of people.