Without knowing the location and capability of primary radar in that region, it is difficult to know if it was even in range of primary radar.
Even if it was in range, it is pretty unlikely it was being tracked in real time by primary radar. At 0600 on a Sunday morning when there is apparently nothing out of the usual to cause the military to be on a higher state of alert? Who would have been looking?
In normal state of alert, the Indonesian National Air Defense Command operate their Early Warning (E/W) radar network for a minimum of 18 hours a day (presumably the hours are on a rotating basis).
No one has to be "looking at" a particular aircraft as radar data are kept for a period of time.
In this case, we have two radar positions of interest. One is the facility at Belitung Island (at the Hanandjoeddin air force base). The second is the Iskandar AFB radar facility at Pangkalanbun, Central Borneo.
From the last known position, both facilities are well within PSR range of even the older Thompson-CSF radars we know the NADC operates. These E/W radars have a range of over 200nm. The NADC also has newer BAE Commander long range surveillance radars.
According to an Air Force spokesman this morning, the AirAsia flight was tracked to its last known position at bearing 247 degrees, 127nm from Pangkalanbun.