The Prime Minister was referred by the Greater London Authority (GLA) on Friday to the police watchdog, the Independent Office for Police Conduct (IOPC), the BBC reported.
The GLA's monitoring officer it had referred Johnson to the IOPC "so it can assess whether or not it is necessary to investigate the former mayor of London for the criminal offence of misconduct in public office".
The GLA added that it has recorded a "conduct matter" against Johnson which happens when there is information that indicates that a criminal offence may have been committed.
But it does not mean that a criminal offence is proved in any way, the GLA's monitoring officer added.
"The IOPC will now consider if it is necessary for the matter to be investigated."
The reason for IOPC's involvment was because the role of the Mayor of London is also London's police and crime commissioner.
The IOPC deals with complaints against police forces in England and Wales.
Responding to the referral, No 10 said: "The Prime Minister, as Mayor of London, did a huge amount of work when selling our capital city around the world, beating the drum for London and the UK.
"Everything was done with propriety and in the normal way," the BBC reported.
The development comes after The Sunday Times said that the businesswoman Jennifer Arcuri joined trade missions Johnson had led and received thousands in sponsorship grants.
Arcuri told the paper that any grants she received and any trade missions she joined were "were purely in respect of my role as a legitimate businesswoman".
Arcuri, a technology entrepreneur, is believed to have moved to London seven years ago, when Johnson was Mayor.
She joined a number of trade missions led by him while in office, and it is understood she attended events on two of these trips - to New York and Tel Aviv - despite not officially qualifying for them as a delegate.
The Sunday Times reported that one of her businesses received 10,000 pounds and 1,500 pounds in sponsorship money from a mayoral organisation when Johnson was Mayor, as well as a 15,000 pounds government grant for foreign entrepreneurs to build businesses in Britain.
( With inputs from IANS )