Strathclyde Police said the men aged 41 and 43, were detained under the Explosives Substances Act 1883 after officers made dawn raids on a number of properties in Kilwinning, Ayrshire, southwest Scotland.
A spokeswoman said the men had not been arrested, but described the detentions as "significant."
"I would like to reassure everyone who lives here that they are not at risk and that we are fully in control of the situation," Chief Superintendent Ruraidh Nicholson said.
Last month, police said parcel bombs sent to Lennon, his lawyer Paul McBride and the former deputy presiding officer of the Scottish parliament Trish Godman could have caused "real harm."
Politicians say the attempted bombings showed action was needed to deal with religious bigotry and sectarian violence between some fans of the club and its city rivals Rangers, which has flared anew in recent months.
Celtic have a predominantly Catholic fan base while city rivals Rangers have mainly Protestant supporters.
Lennon, a Northern Irish Catholic, who has been the subject of several threats and physical abuse in the past, has himself been blamed for stoking the tensions, along with senior figures at Rangers.
On Wednesday, Lennon was at the centre of another controversial incident when he was attacked by a fan during his team's 3-0 Scottish Premier League victory over Hearts in Edinburgh.
Scottish police said on Thursday they had detained a man in connection with the alleged assault.
