It is absolutely possible. Scanning is just another form of input. Generally you would have your scanner configured to append a tab character to the input. I have done scanning since version 5.
Most barcode scanners operate in keyboard emulation mode which means your computer percieves the scanned data just as though a user and typed in the data. You can consider the barcode as text that has been formatted in a font your scanner can read but you can't.
Thus, you can simply place the cursor in a filemaker field and scan your bar code. If you want to trigger filemaker to do something immediatedly after the scan, you can program most scanners to append a "postamble" character to the end of the scanned data that can be a tab, enter or return character. In filemaker 10, you can use any one of these characters to trigger an OnObjectExit script trigger on your field. With older versions of Filemaker, you can use the Enter character as your postamble and use it to continue a paused script to process the scanned data.
For more on the subject, use the advanced search link above and search for threads on the subject, using barcode as your key word.