Unlikely. The main culprits in high battery usage are the screen, the gps, and the radio when there's not very much signal. Google Now does not ever show up in my top-five battery users list.
You could also try this: if Google Now is waking your phone up any significant portion of the time, it'll show up in the list as a low percentage app. You can click on it to see how much time it's keeping the CPU awake, keeping the screen on, using the GPS, etc. I believe Google Now processing is accounted to the Google Search app (because that is where all its output shows up). On my phone, which has Google Now enabled, it shows zero active time for GPS, screen awake, CPU, etc.
Interestingly, GSam battery monitor (which I just got last week, and is really neat!) shows the number of times each app woke the device. I've been on for 4.5 hours, and Maps is at 441, with the next Android System at 85 and Google Search (which is Now) at 53.
Android System has also shown up more in usage % since I started having Now.
I think there's definitely a significant drain with Now. I've had it enabled since the Verizon release, somewhere around 12/20, but I think I will disable it at the start of next month and keep an eye on how it behaves. I certainly feel that my battery life has gone down since the upgrade.