How to remove the extra frame around my text box in InDesign?

As Barbara explained, your text frame has a text wrap applied. To remove the text wrap click once to select the frame. Next, open the Text Wrap panel and click on the leftmost icon to reset the offset to None.

If this problem persists the next time you create a text frame you'll need to reset the Type tool itself. Select the Type tool but don't click-drag to create a text frame. Select it only. Go back to the Text Wrap panel where you'll see that some kind of text wrap has been permanently applied. Click on the None icon as I instructed above to remove this baked-in setting. Finally, click on the black arrow tool. The Type Tool should now be reset.

If the Type Tool continues to apply a text wrap automatically, the problem is will be found in your Object Styles. Let me know if need help to reset those Styles.

To remove a text wrap, select the frame with the black Selection tool. Open the Text Wrap panel and click the first icon in the top row.

It looks like the text frame may have a text wrap applied to it.