It depends. You can scan a QR Code if your smartphone camera decodes them, or you install a QR Code scanner App. However, depending on the QR Code type you may not have access to its content without an internet connection.
Static QR Codes work without an internet connection
A static QR Code does NOT require internet access because the contents are encoded within the QR Code. They are also known as offline QR Codes.
Here are some examples of QR Code types that can be read without an internet connection.
vCard QR Codes
vCard QR Codes contain contact information in the QR Code. By scanning the QR code, the contact can be added directly to the address book without having to connect to the Internet.
Wi-Fi QR Codes
If you don't have an internet connection, you can connect to the internet using a Wi-Fi QR code.
GPS QR Codes
GPS coordinates stored in a QR code can lead you to a location on a map, provided the map material is stored offline on your smartphone.
Event QR Codes
Event QR Codes containing information about an event can be added directly to your calendar after scanning.
Text QR Codes
Text QR codes contain a simple text message and can be read and displayed directly on the smartphone without an internet connection.
Dynamic QR Codes require an internet connection
A dynamic QR Code requires access to the internet because the encoded information is a URL, and it is followed after scanning the QR Code.
If you scan a dynamic QR Code without an internet connection available, you will get an error message just like if you were trying to visit a webpage without having access to the Internet.