Marco Rubio to Announce 2016 Presidential Run Decision on April 13

— -- Republican Sen. Marco Rubio said today he will announce whether he will run for president at an upcoming event.

“I will announce on April 13 what I’m going to do next in terms of running for president or the U.S. Senate," Rubio said on FOX News' "The Five."

Rubio, a first-term senator, is up for re-election to the Senate in 2016, but Florida law bars him from running for both the Senate and the presidency at the same time. If he chooses to run for president but loses, Rubio said he wouldn't fall back on a Senate bid as a back-up plan.

"When you choose to do something as big as that, you’ve really got to be focused on that and not have an exit strategy," Rubio said earlier this year.

One of Rubio's potential presidential opponents, Sen. Rand Paul, R-Kentucky, is planning on running for both offices in 2016. Earlier this month, Sen. Ted Cruz, R-Texas, became the first major presidential candidate to declare a 2016 presidential bid.

Should Rubio decide to run for president, he will likely face his old mentor -- former Florida Gov. Jeb Bush. Asked to assess how Bush's expected candidacy could affect his own race, Rubio said, "The time will come for comparison shopping."

Rubio also commented on former Secretary of State Hillary Clinton's use of a private email server for official business, saying it must be determined if she sent sensitive information using the private email.

"I think she has bigger problems than emails. Ultimately I don’t think she has an agenda that looks forward to the 21st century," Rubio said.

Rubio revealed he uses a private email of his own, but stressed that he never includes "sensitive" information in his messages.

"I don’t write anything that’s national security related in an email," Rubio said.

ABC News' Michael Falcone contributed to this report.