Two men in their 20s were rushed to a hospital after emergency services responded to reports of a bomb explosion in the west of the capital just after 8:30 p.m. CT.
Police told a press conference that the wounded men were taken to a hospital, but their injuries were not life threatening. They added that the explosion may have been detonated by a trip wire.
"We have a scene where it is obvious an explosion has taken place," Austin Police Chief Brian Manley said. "We just simply do not know a lot at this point."
"Given that there may have been a different triggering mechanism in this device, we wanted to get that out as early as possible," Manley later added.
He also told people to stay in their homes and avoid touching any suspicious packages, but did not say whether there was any link between the latest blast and the earlier parcel bombs.
The FBI said on Twitter that its agents were at the scene of Sunday's explosion in a residential neighborhood on the west side of the city, several miles from the east side neighborhoods where the earlier blasts occurred.
"Residents in immediate area ... wait in your homes and follow instructions of officers," Austin police said on their Twitter feed.
A string of explosions have already killed two men and left a further two women with injuries.
Thirty-nine-year-old Anthony Stephan House died on Mar. 2 after a device detonated on his front porch and
Mason's 40-year-old mother was left injured by the explosion and 75-year-old Esperanza Morena Herrera was sent to a hospital after a separate explosion at her home on Mar. 12.
Police have said they believe the explosions are connected and possibly-race related. All of the victims have been African-American or Hispanic.
In a press conference a few hours ahead of the Sunday evening explosion, Austin Police Chief Brian Manley said: "We believe that the recent explosive incidents that have occurred in the city of Austin were meant to send a message."
"The person or persons understands what that message is and are responsible for constructing or delivering the devices and we hope this person or persons is watching and will reach out to us before anyone else is injured or anyone else is killed out of this event," he said.
Over 500 federal agents are involved in the investigation and authorities continue to ask the local community for assistance.
They are offering a reward of $115,000 for information leading to the arrest of those responsible.
The bombings have also led to a surge in the number of suspicious packages reported in recent weeks. Police have responded to 735 related calls since the explosions were first reported at the start of this month.
—Reuters contributed to this report.