A bomb disposal unit has been deployed to the site of incident, according to local media reports.
The suspicious package was discovered in one of the ladies' compartments of a Puttalam-Mount Lavinia train, according to reports.
Police have confirmed that nothing suspicious was found in the parcel at Kollupitiya Railway Station.
On Sunday, the country was shaken by a series of coordinated attacks, which killed at least 310 people and left another 500 injured. These are the worst attacks in the country's modern history since the end of the 25-year-old civil war.
Colombo has launched a massive security operation in the wake of the tragedy. As of Monday, at least 24 people were detained in connection with the attacks.