As part of the investigation, a CCTV still of the man police would like to speak to has been issued in a bid to identify him.
The first incident happened on Saturday July 2 at around 2am on a N18 bus.
A 27-year-old woman was travelling on the bus and fell asleep. She was woken by an unknown man who was sitting next to her and touching her. The victim pushed the man away before getting off the bus and calling police.
Three similar incidents occurred on route 226 buses across Brent between July 17 and September 21.
On July 17 a 21-year-old woman boarded the bus at around 9am. The suspect came and sat next to her and began touching her leg. The victim got off the bus at Acton Lane in Harlesden and called police.
The next incident happened at approximately 3.10pm on August 8. A 27-year-old woman was sitting on the bus when the suspect came and sat next to her. He began touching himself before the victim got up and left the bus in High Street, Harlesden.
The most recent incident occurred on a September 21 at around 5pm. The victim, a 31-year-old woman, was approached by the suspect as she sat on the bus. The man sat next to her and touched her before he was challenged by the woman. The suspect got up and left the bus at Park Royal station.
Following a police investigation, officers believe that all of the offences were carried out by the same man.
The man is described as of Middle Eastern appearance, about 30 to 35 years old, 5ft 7in tall and of a slim build.
Anyone who has information that could assist the investigation is asked to contact Detective Constable Annie Garrard or Detective Constable Teresa Moore from the RPTC on 101. Alternatively, you can call Crimestoppers anonymously on 0800 555 111.