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Is power always on to the oxygen sensor heater? (1998 Maxima)

I know that the O2 sensor has a heater to get it to operating temperature quickly. Is the heater always powered on when you are driving or does the computer shut it off after the engine (and O2 sensor ) get fully warmed up?

Thanks in advance

The oxygen sensor heaters are switched ON when the ignition switch is turned to ON, and then, after a few seconds, or a couple of minuets, they are turned OFF. Difference in the ON times varies from make to make (and, from model year, to model year).
The PCM (engine computer) is the “switch” (driver circuit) for the oxygen sensor heater. It makes the ground path for the circuits, when it switches the heater ON.

Besides warmup, the Maxima will also turn on the sensor heat when the engine is idling.