The House of Commons’ Parliamentary Digital Service said it was investigating the issue and had put measures in place to prevent unauthorised access to Mr O’Mara's parliamentary account.
It comes after his chief of staff, Gareth Arnold, said he was working for the MP without being vetted by Parliament.
The Star understands he had access to the MP's casework, including constituents’ personal information.
Mr O’Mara’s website and Twitter account have both been deleted, along with that of Mr Arnold, who quit in sensational fashion by posting a damning and foul-mouthed rant on the MP’s own Twitter account.
In a statement, the House of Commons said: “We are aware of allegations relating to the misuse of a parliamentary network account and are investigating the issue.
“Measures are in place to prevent unauthorised access to Mr O’Mara’s parliamentary account.”
The Star exclusively revealed how Mr O’Mara stated he intended to resign following the MP’s summer recess on September 3, following his most damning week of a turbulent two years in office.
Mr Arnold’s Twitter rant was followed by 20-year-old Jennifer Barnes, employed by the politician, accusing him of sexual harassment.
The MP, aged 37, said he was ‘not well and in the process of receiving medical help’ and would tender his resignation ‘via the official Parliamentary process' as soon as term restarts.
When The Star visited Mr O’Mara’s city centre office on Tuesday, it was told it was now ‘vacant’.
Mr O’Mara has cerebral palsy and is autistic.
Following his election in 2017 he enjoyed a brief honeymoon period, during which he pledged to be a champion for disability rights.
But a short time later, misogynistic and homophobic posts surfaced that he had made online as a younger man, and his reputation in Hallam – and the political arena generally – never recovered.
He resigned from the Labour party in July 2018 and has stood as an independent since.
The House of Commons’ Parliamentary Commissioner for Standards, who investigates alleged breaches of the Code of Conduct for MPs, said it could not confirm or deny whether the conduct of any named MP was under investigation as investigations were ‘private’.
Neither Mr O’Mara or Mr Arnold responded to The Star’s request for a comment.