According to Official Guinness Records,
The longest continuous ride standing on the seat of a motorcycle is 32.3 km (20 miles) and was achieved by Ratnesh Pandey (India), in Indore, Madhya Pradesh, India on 5 December 2015. Ratnesh rode a Honda Unicorn for this attempt. As per the rules, he did not touch the handlebars at any time during his ride.
For a complete list of 2015 records, please visit 2015 Guinness Records in India.