He fell ill at around 2.30pm during the journey to the free ticketed event taking place across the Bank Holiday weekend.
Emergency crews rushed the lad to Hull Royal Infirmary but he could not be saved and died later that afternoon.
In a statement, Humberside Police said: “A 20-year-old man has been arrested in connection with the sad death of a 21-year-old man yesterday.
“The man died at Hull Royal Infirmary after being taken ill on a bus travelling from Hull’s Paragon Interchange to Burton Constable Hall.
“We are continuing our investigation into the circumstances of his death today but they are not believed to be suspicious.
“A 20-year-old man arrested in connection with the investigation remains in police custody.
A woman in the crowd in front of the main stage
“A 20-year-old man has been arrested in connection with the sad death of a 21-year-old man yesterday.”
More than 50,000 music fans are expected to flock to the festival to see the likes of Katy Perry, Kasabian and Emile Sande.
it is held once a year and is the biggest free ticketed festival in Europe.