Sombat Ornsomboon, chief of Kamphaeng Saen police station, said the bomb was likely left there on Sunday night. It was found and then safely detonated by police on Monday, the INN news agency reported.
Pol Col Sombat did not give any further details of the bomb, but said he thought it was possibly a threat to Luang Pu ahead of his planned return to Wat Or Noi on Monday.
The monk was due to stay at the temple on Monday night and return to his protest base on Chaeng Wattana Road on Tuesday.
Meanwhile, police said they still had no leads on who made the latest attacks at the anti-government protest base controlled by the monk.
Pol Col Kamtorn Ouichareon, chief of the Explosive Ordnance Disposal unit, said on Monday that police investigators could not determine where the two M79 grenade rounds were fired from. One hit the People's Democratic Reform Committee (PDRC) stage and the other landed inside the compound of the Anti-aircraft Artillery Division nearby at 10pm on Sunday.
The PDRC stage in the area has been the presumed target of M79 grenades several times.
Lung Pu believed the gtrenades on Sunday night were aimed at his temporary residence on Chaeng Wattana but missed the target.
Two grenades were also fired at the rally site of the Network of Students and People for the Reform of Thailand (NSPRT) near Government House on Phitsanulok road in Bangkok on Saturday night and another one at a Rangsit University building in Pathum Thani on Sunday.
Former Election Commission secretary-general Pirun Chatwanichkul called for serious efforts from police and soldiers to stop the grenade attacks.
''The attacks could be stopped if intelligence officials do their work,'' he told INN radio news channel.
''It should not be difficult to find out who is behind these attacks, but security authorities have no measures in place to prevent the attacks at all,'' he said.
Nasser Yeema, chief of the NSPRT guards, said last week that he expected the violence to increase after the PDRC launched its "final battle'' to bring down the caretaker government.