The service at the memorial cairn in Arlington Cemetery, Washington DC, will take place at the local time (3.03pm) the events of December 21, 1988 unfolded over the Scottish town, which happened at 7.03pm UK time. Britain's worst terrorist atrocity killed 270 people, 189 of whom were American citizens.
Also attending will be Frank Mulholland, the Lord Advocate, Eric Holder, the US Attorney General, and Robert Mueller, the outgoing director of the FBI.
As it is the 25th anniversary, the expectation is that a large number of relatives of the victims will attend.
Mr Mundell, who is also the MP for Lockerbie, said: "A number of people are making a special effort to come to this particular event." For example, there will be a sizeable group from Syracuse University; 35 students from the New York college were among the victims.
He added: "Over the years an enormous amount has been focused on the perpetrators of this event, but we still need to give far more thought to the families and friends of those killed and all those other people caught up on the night and in the aftermath.
"Nobody thinks that just because it's 25 years that will draw a line under it. It is another milestone; most people think it's hard to believe 25 years have passed since that dreadful night."
Memorial services will also be held on Saturday week at Westminster Abbey and in Lockerbie, again at the same time of day the tragedy struck.
Meanwhile, the Justice For Megrahi group has repeated its call for the courts to look again at the case of the late Libyan, who to date has been the only person convicted of the crime.
Detectives from Police Scotland continue to investigate the bombing, but no new evidence in the case has been made public.