The investigation concerns events which took place in August 2010 after a Swedish woman met the Australian at a WikiLeaks conference in Stockholm.
Assange has always denied the allegation.
In a statement, the prosecution agency said it was planning a press conference on Tuesday at 2pm when the prosecutor will give a briefing on the “investigative measures taken” and “provide new information”.
The 48-year-old has been held at a top-security British prison since April after police dragged him out of the Ecuadoran embassy in London, where he had been holed up since 2012 to avoid an extradition order to Sweden.
Assange was subsequently sentenced to 50 weeks in prison for breaching bail conditions when he took refuge in the embassy.
Following his arrest, Swedish authorities reopened their 2010 rape investigation, which had been closed in 2017 on the argument it was not possible to proceed with the probe as Assange could not be reached.
In September, prosecutors said they had interviewed seven witnesses over the summer and that Assange was suspected of rape.
Swedish deputy director of public prosecutions Eva-Marie Persson – in charge of the investigation – also said the material from the interviews was to be analyzed further before she decided on how to protest.
Assange is currently also the subject of a US extradition request to face charges relating to obtaining and disseminating classified information over the publishing of military documents and diplomatic cables through the WikiLeaks website.
Since his April arrest, questions regarding Assange's health have been raised, with him appearing frail and confused at court hearings.
'Die in jail'
Earlier in November, John Shipton, Assange's father, warned that his son “may die in jail”.
His comments followed a warning from the UN's Speical Rapporteur on Torture, Nils Melzer, who said that the treatment of Assange was putting his life “at risk”.
Swedish judge Nils Petter Ekdahl told AFP that the prosecutor has a duty to try and bring a suspect to justice if the evidence warrants it.
“If you believe there is enough evidence for a conviction, even in an old case, the principal rule is to charge the person,” Ekdahl said.
Ekdahl added that the prosecutor can under certain circumstances make exceptions to this rule. It could for instance be decided that even if a conviction is likely the sentence would probably be lenient owing to Assange's poor health – and therefore decide not to pursue the case.
The statute of limitations in the case expires in August 2020.