The alert centred on the Cornakinnegar Road area of Lurgan.
Detectives investigating violent dissident republican activity conducted a search in the area and have recovered a quantity of bomb making material and ammunition.
The items have been taken away for further examination.
The train line between Lurgan and Moira has now re-opened.
Detective Inspector Adrian Brown from PSNI Serious Crime Branch said: “I am pleased to have removed these deadly items from the hands of ruthless and dangerous individuals.
“Our enquiries will continue and I would ask anyone with any information which could assist us to contact police on 101.
“Or alternatively, information can also be provided to the independent charity Crimestoppers on 0800 555 111 which is 100% anonymous and gives people the power to speak up and stop crime.”