Public Health England (PHE) told the Bristol Post it was investigating the diagnosis at Boardmasters festival in Newquay, Cornwall.
The teenager is a student at St Brendan's Sixth Form College in Bristol.
Festival organisers said he had been unwell in the days before the event.
The student's college has had two cases of meningococcal infection since the spring of 2016.
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Deputy director of health protection at PHE's South West Health Protection Team, Mike Wade, said his thoughts were with the family of the critically ill patient.
"We want to reassure people that all appropriate public health actions are being taken," he said.
"It is highly unlikely that this case is related to the previous cases at St Brendan's which occurred 14 months ago.
"The student has not attended the college since the end of the summer term at the beginning of July."
Those in close contact with him at the festival were offered antibiotics.
What is meningitis?
Source: NHS Choices
It is not known if the man contracted the disease at the festival, but administering antibiotics to close contacts was "standard procedure" with confirmed cases of meningitis, PHE said.
The organisers and medical teams at Boardmasters Festival confirmed an 18-year-old was transferred to a hospital in Cornwall after being treated on site.
Dr Aaron Pennell, medical director of Emergency Doctor Medical Services, which was providing medical support at the festival said the teenager was seen and assessed by two intensive care doctors and two critical care paramedics who were part of the medical team on the site.
"The patient was assessed fully including initial blood and urine tests to identify life-threatening illness that were all initially negative," he said.
"He was transferred with a doctor and paramedic to hospital after his condition deteriorated after transfer to a welfare area."
The surfing and music festival ran from Wednesday 9 August to Sunday.
Festival-goers in close contact with an 18-year-old who became critically ill with meningitis have been given antibiotics.