Two men and a woman were arrested in Keighley this morning (May 1) as part of a raid carried out by Counter Terrorism Policing North East.
Two addresses are currently being searched in Keighley in relation to the investigation, but police have not revealed their location.
The two men and woman were taken to a police station in West Yorkshire for questioning.
A statement from West Yorkshire Police said: "Following the discovery of potentially suspicious material at one of the addresses in Keighley the Explosive Ordnance Disposal Unit (EOD) has been called to provide specialist advice and to arrange the safe removal of the items if required.
"As a precautionary measure, a cordon has been put in place and a number of local residents have evacuated whilst examinations are conducted.
"We recognise that local people may have concerns as a result of this activity. We would like to reassure them that these arrests are pre-planned and intelligence led and there is not believed to be any immediate risk to the local community. We are grateful for the understanding, patience and support of local residents while these enquiries continue."
A 28 year old man from North Wales and a 16 year old male from Wiltshire have also been arrested on suspicion of the same offences as part of this investigation.