Hi Saratraverz!
This is actually a setting on the mobile device itself, rather than an Axure-level setting. The text field widget turns into a real HTML form element in the browser, so if you’re using a Text Field widget, for example, the device recognizes it as an element that takes text input.
For iOS, you can turn off predictive text by navigating to “Settings > General > Keyboards”. For Android, it seems like there are a few different ways to turn off predictive text, depending on the Android device you are using: